Virtualization Guide - Guide to Virtualization on Red Hat ...fcs/Doc/RedHat/Red_Hat_Enterprise_Linux-6... · Red Hat Enterprise Linux 6 Virtualization Guide Guide to Virtualization

Red Hat Enterprise Linux 6

Virtualization GuideGuide to Virtualization on Red Hat Enterprise Linux 6

Virtualization Guide

Red Hat Enterprise Linux 6 Virtualization GuideGuide to Virtualization on Red Hat Enterprise Linux 6Edition 1

Author

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The Red Hat Enterprise Linux Virtualization Guide contains information on installation, configuring,administering, and troubleshooting virtualization technologies included with Red Hat Enterprise Linux.

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Preface vii1. Document Conventions .................................................................................................. vii

1.1. Typographic Conventions .................................................................................... vii1.2. Pull-quote Conventions ........................................................................................ ix1.3. Notes and Warnings ............................................................................................ ix

2. We need your feedback .................................................................................................. x

1. Introduction 11.1. What is virtualization? .................................................................................................. 11.2. KVM and virtualization in Red Hat Enterprise Linux ........................................................ 11.3. libvirt and the libvirt tools .............................................................................................. 21.4. Virtualized hardware devices ........................................................................................ 2

1.4.1. Virtualized and emulated devices ....................................................................... 31.4.2. Para-virtualized drivers ...................................................................................... 41.4.3. Physically shared devices .................................................................................. 5

1.5. Storage ........................................................................................................................ 61.6. Virtualization security features ....................................................................................... 71.7. Migration ...................................................................................................................... 71.8. V2V ............................................................................................................................. 8

I. Requirements and limitations 9

2. System requirements 11

3. KVM compatibility 13

4. Virtualization limitations 154.1. General limitations for virtualization ..................................................................... 154.2. KVM limitations .................................................................................................. 154.3. Application limitations ......................................................................................... 16

II. Installation 19

5. Installing the virtualization packages 215.1. Installing KVM with a new Red Hat Enterprise Linux installation ............................. 215.2. Installing KVM packages on an existing Red Hat Enterprise Linux system ............... 25

6. Virtualized guest installation overview 276.1. Virtualized guest prerequisites and considerations ................................................ 276.2. Creating guests with virt-install ............................................................................ 276.3. Creating guests with virt-manager ....................................................................... 286.4. Installing guests with PXE ................................................................................... 37

7. Installing Red Hat Enterprise Linux 6 as a virtualized guest 437.1. Creating a Red Hat Enterprise Linux 6 guest with local installation media ............... 437.2. Creating a Red Hat Enterprise Linux 6 guest with a network installation tree ........... 537.3. Creating a Red Hat Enterprise Linux 6 guest with PXE ......................................... 55

8. Installing Red Hat Enterprise Linux 6 as a para-virtualized guest on Red HatEnterprise Linux 5 59

8.1. Using virt-install .................................................................................................. 598.2. Using virt-manager ............................................................................................. 60

9. Installing a fully-virtualized Windows guest 719.1. Using virt-install to create a guest ....................................................................... 719.2. Installing Windows 2003 ..................................................................................... 72


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III. Configuration 73

10. Network Configuration 7510.1. Network Address Translation (NAT) with libvirt .................................................... 7510.2. Bridged networking with libvirt ........................................................................... 76

11. KVM Para-virtualized Drivers 7911.1. Using the para-virtualized drivers with Red Hat Enterprise Linux 3.9 guests ........... 7911.2. Installing the KVM Windows para-virtualized drivers ............................................ 82

11.2.1. Installing the drivers on an installed Windows guest .................................. 8211.2.2. Installing drivers during the Windows installation ...................................... 92

11.3. Using KVM para-virtualized drivers for existing devices ....................................... 9911.4. Using KVM para-virtualized drivers for new devices ........................................... 100

12. PCI passthrough 10712.1. Adding a PCI device with virsh ........................................................................ 10812.2. Adding a PCI device with virt-manager ............................................................. 11012.3. PCI passthrough with virt-install ....................................................................... 114

13. SR-IOV 11713.1. Introduction .................................................................................................... 11713.2. Using SR-IOV ................................................................................................. 11813.3. Troubleshooting SR-IOV .................................................................................. 121

14. KVM guest timing management 123

IV. Administration 127

15. Server best practices 129

16. Security for virtualization 13116.1. Storage security issues ................................................................................... 13116.2. SELinux and virtualization ............................................................................... 13116.3. SELinux ......................................................................................................... 13316.4. Virtualization firewall information ...................................................................... 133

17. sVirt 13517.1. Security and Virtualization ............................................................................... 13617.2. sVirt labeling ................................................................................................... 136

18. KVM live migration 13918.1. Live migration requirements ............................................................................ 13918.2. Shared storage example: NFS for a simple migration ........................................ 14018.3. Live KVM migration with virsh ......................................................................... 14118.4. Migrating with virt-manager ............................................................................. 142

19. Remote management of virtualized guests 15519.1. Remote management with SSH ....................................................................... 15519.2. Remote management over TLS and SSL ......................................................... 15619.3. Transport modes ............................................................................................. 157

20. Overcommitting with KVM 161

21. KSM 165

22. Advanced virtualization administration 16922.1. Guest scheduling ............................................................................................ 16922.2. Advanced memory management ...................................................................... 16922.3. Guest block I/O throttling ................................................................................. 16922.4. Guest network I/O throttling ............................................................................. 169

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23. Migrating to KVM from other hypervisors using virt-v2v 17123.1. Preparing to convert a virtualized guest ........................................................... 17123.2. Converting virtualized guests ........................................................................... 175

23.2.1. virt-v2v ................................................................................................ 17523.2.2. Converting a local Xen virtualized guest ................................................ 17723.2.3. Converting a remote Xen virtualized guest ............................................. 17723.2.4. Converting a VMware ESX virtualized guest .......................................... 17723.2.5. Converting a virtualized guest running Windows ..................................... 178

23.3. Running converted virtualized guests ............................................................... 17923.4. Configuration changes .................................................................................... 179

23.4.1. Configuration changes for Linux virtualized guests .................................. 17923.4.2. Configuration changes for Windows virtualized guests ............................ 180

24. Miscellaneous administration tasks 18324.1. Automatically starting guests ........................................................................... 18324.2. Using qemu-img ............................................................................................. 18324.3. Verifying virtualization extensions ..................................................................... 18424.4. Setting KVM processor affinities ...................................................................... 18524.5. Generating a new unique MAC address ........................................................... 18924.6. Improving guest response time ........................................................................ 19024.7. Very Secure ftpd ......................................................................................... 19124.8. Disable SMART disk monitoring for guests ....................................................... 19224.9. Configuring a VNC Server ............................................................................... 19224.10. Gracefully shutting down guests .................................................................... 19224.11. Virtual machine timer management with libvirt ................................................. 193

V. Virtualization storage topics 197

25. Storage concepts 19925.1. Storage pools ................................................................................................. 19925.2. Volumes ........................................................................................................ 200

26. Storage pools 20326.1. Creating storage pools ................................................................................... 203

26.1.1. Dedicated storage device-based storage pools ...................................... 20326.1.2. Partition-based storage pools ................................................................ 20526.1.3. Directory-based storage pools ............................................................... 21126.1.4. LVM-based storage pools ..................................................................... 21726.1.5. iSCSI-based storage pools ................................................................... 22326.1.6. NFS-based storage pools ..................................................................... 232

27. Volumes 23727.1. Creating volumes ............................................................................................ 23727.2. Cloning volumes ............................................................................................. 23727.3. Adding storage devices to guests .................................................................... 238

27.3.1. Adding file based storage to a guest ..................................................... 23827.3.2. Adding hard drives and other block devices to a guest ............................ 240

27.4. Deleting and removing volumes ....................................................................... 241

28. Miscellaneous storage topics 24328.1. Creating a virtualized floppy disk controller ....................................................... 24328.2. Configuring persistent storage in Red Hat Enterprise Linux 6 ............................. 24428.3. Accessing data from a guest disk image .......................................................... 247

29. N_Port ID Virtualization (NPIV) 25129.1. Enabling NPIV on the switch ........................................................................... 251


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29.1.1. Identifying HBAs in a Host System ........................................................ 25129.1.2. Verify NPIV is used on the HBA ............................................................ 252

VI. Virtualization reference guide 255

30. Managing guests with virsh 257

31. Managing guests with the Virtual Machine Manager (virt-manager) 26731.1. Starting virt-manager ....................................................................................... 26731.2. The Virtual Machine Manager main window ...................................................... 26831.3. The virtual hardware details window ................................................................ 26931.4. Virtual Machine graphical console .................................................................... 27131.5. Adding a remote connection ............................................................................ 27331.6. Displaying guest details .................................................................................. 27431.7. Performance monitoring .................................................................................. 28131.8. Displaying CPU usage .................................................................................... 28331.9. Displaying Disk I/O ......................................................................................... 28431.10. Displaying Network I/O .................................................................................. 28531.11. Managing a virtual network ............................................................................ 28631.12. Creating a virtual network .............................................................................. 288

32. libvirt configuration reference 297

33. Creating custom libvirt scripts 29933.1. Using XML configuration files with virsh ........................................................... 299

VII. Troubleshooting 301

34. Troubleshooting 30334.1. Debugging and troubleshooting tools ............................................................... 30334.2. kvm_stat ........................................................................................................ 30434.3. Log files ......................................................................................................... 30734.4. Troubleshooting with serial consoles ................................................................ 30734.5. Virtualization log files ...................................................................................... 30834.6. Loop device errors .......................................................................................... 30834.7. Enabling Intel VT and AMD-V virtualization hardware extensions in BIOS ............ 30834.8. KVM networking performance .......................................................................... 309

A. Additional resources 311A.1. Online resources ...................................................................................................... 311A.2. Installed documentation ............................................................................................ 311

Glossary 313

B. Revision History 317

C. Colophon 319

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PrefaceWelcome to the Red Hat Enterprise Linux 6 Virtualization Guide. This guide covers all aspects of usingand managing virtualization products included with Red Hat Enterprise Linux 6.

This book is divided into 7 parts:• System Requirements

• Installation

• Configuration

• Administration

• Reference

• Troubleshooting

• Appendixes

Key terms and concepts used throughout this book are covered in the Glossary.

1. Document ConventionsThis manual uses several conventions to highlight certain words and phrases and draw attention tospecific pieces of information.

In PDF and paper editions, this manual uses typefaces drawn from the Liberation Fonts1 set. TheLiberation Fonts set is also used in HTML editions if the set is installed on your system. If not,alternative but equivalent typefaces are displayed. Note: Red Hat Enterprise Linux 5 and later includesthe Liberation Fonts set by default.

1.1. Typographic ConventionsFour typographic conventions are used to call attention to specific words and phrases. Theseconventions, and the circumstances they apply to, are as follows.

Mono-spaced Bold

Used to highlight system input, including shell commands, file names and paths. Also used to highlightkeycaps and key combinations. For example:

To see the contents of the file my_next_bestselling_novel in your currentworking directory, enter the cat my_next_bestselling_novel command at theshell prompt and press Enter to execute the command.

The above includes a file name, a shell command and a keycap, all presented in mono-spaced boldand all distinguishable thanks to context.

Key combinations can be distinguished from keycaps by the hyphen connecting each part of a keycombination. For example:

Press Enter to execute the command.

1 https://fedorahosted.org/liberation-fonts/

https://fedorahosted.org/liberation-fonts/

https://fedorahosted.org/liberation-fonts/

Preface

viii

Press Ctrl+Alt+F2 to switch to the first virtual terminal. Press Ctrl+Alt+F1 toreturn to your X-Windows session.

The first paragraph highlights the particular keycap to press. The second highlights two keycombinations (each a set of three keycaps with each set pressed simultaneously).

If source code is discussed, class names, methods, functions, variable names and returned valuesmentioned within a paragraph will be presented as above, in mono-spaced bold. For example:

File-related classes include filesystem for file systems, file for files, and dir fordirectories. Each class has its own associated set of permissions.

Proportional Bold

This denotes words or phrases encountered on a system, including application names; dialog box text;labeled buttons; check-box and radio button labels; menu titles and sub-menu titles. For example:

Choose System → Preferences → Mouse from the main menu bar to launch MousePreferences. In the Buttons tab, click the Left-handed mouse check box and clickClose to switch the primary mouse button from the left to the right (making the mousesuitable for use in the left hand).

To insert a special character into a gedit file, choose Applications → Accessories→ Character Map from the main menu bar. Next, choose Search → Find… from theCharacter Map menu bar, type the name of the character in the Search field and clickNext. The character you sought will be highlighted in the Character Table. Double-click this highlighted character to place it in the Text to copy field and then click the

Copy button. Now switch back to your document and choose Edit → Paste from thegedit menu bar.

The above text includes application names; system-wide menu names and items; application-specificmenu names; and buttons and text found within a GUI interface, all presented in proportional bold andall distinguishable by context.

Mono-spaced Bold Italic or Proportional Bold Italic

Whether mono-spaced bold or proportional bold, the addition of italics indicates replaceable orvariable text. Italics denotes text you do not input literally or displayed text that changes depending oncircumstance. For example:

To connect to a remote machine using ssh, type ssh [email protected] ata shell prompt. If the remote machine is example.com and your username on thatmachine is john, type ssh [email protected].

The mount -o remount file-system command remounts the named filesystem. For example, to remount the /home file system, the command is mount -oremount /home.

To see the version of a currently installed package, use the rpm -q packagecommand. It will return a result as follows: package-version-release.

Note the words in bold italics above — username, domain.name, file-system, package, version andrelease. Each word is a placeholder, either for text you enter when issuing a command or for textdisplayed by the system.

Aside from standard usage for presenting the title of a work, italics denotes the first use of a new andimportant term. For example:

Pull-quote Conventions

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Publican is a DocBook publishing system.

1.2. Pull-quote ConventionsTerminal output and source code listings are set off visually from the surrounding text.

Output sent to a terminal is set in mono-spaced roman and presented thus:

books Desktop documentation drafts mss photos stuff svnbooks_tests Desktop1 downloads images notes scripts svgs

Source-code listings are also set in mono-spaced roman but add syntax highlighting as follows:

package org.jboss.book.jca.ex1;

import javax.naming.InitialContext;

public class ExClient{ public static void main(String args[]) throws Exception { InitialContext iniCtx = new InitialContext(); Object ref = iniCtx.lookup("EchoBean"); EchoHome home = (EchoHome) ref; Echo echo = home.create();

System.out.println("Created Echo");

System.out.println("Echo.echo('Hello') = " + echo.echo("Hello")); }}

1.3. Notes and WarningsFinally, we use three visual styles to draw attention to information that might otherwise be overlooked.

Note

Notes are tips, shortcuts or alternative approaches to the task at hand. Ignoring a note shouldhave no negative consequences, but you might miss out on a trick that makes your life easier.

Important

Important boxes detail things that are easily missed: configuration changes that only apply tothe current session, or services that need restarting before an update will apply. Ignoring a boxlabeled 'Important' will not cause data loss but may cause irritation and frustration.

Warning

Warnings should not be ignored. Ignoring warnings will most likely cause data loss.

Preface

x

2. We need your feedbackIf you find a typographical error in this manual, or if you have thought of a way to make this manualbetter, we would love to hear from you. Submit a report in Bugzilla: http://bugzilla.redhat.com/ againstthe Red_Hat_Enterprise_Linux product.

When submitting a bug report, be sure to refer to the correct component: doc-Virtualization_Guide andversion number: 6.

If you have a suggestion for improving the documentation, try to be as specific as possible whendescribing it. If you have found an error, include the section number and some of the surrounding textso we can find it easily.

http://bugzilla.redhat.com/

Chapter 1.

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IntroductionThis chapter introduces various virtualization technologies, applications and features and explains howthey work. The purpose of this chapter is to assist Red Hat Enterprise Linux users in understandingthe basics of virtualization.

1.1. What is virtualization?Virtualization is a broad computing term for running software, usually operating systems, concurrentlyand isolated from other programs on one system. Most existing implementations of virtualization use ahypervisor, a software layer that controls hardware and provides guest operating systems with accessto underlying hardware. The hypervisor allows multiple operating systems to run on the same physicalsystem by offering virtualized hardware to the guest operating system. There are various methods forvirtualizing operating systems:

• Hardware-assisted virtualization is the technique used for full virtualization with KVM.

• Para-virtualization is a technique used by Xen to run Linux guests.

• Software virtualization or emulation. Software virtualization uses binary translation and otheremulation techniques to run unmodified operating systems. Software virtualization is significantlyslower than hardware-assisted virtualization or para-virtualization. Software virtualization, usingQEMU without KVM, is unsupported by Red Hat Enterprise Linux.

1.2. KVM and virtualization in Red Hat Enterprise Linux

What is KVM?(KVM) is a Full virtualization solution for Linux on AMD64 and Intel 64 hardware. KVM is a Linuxkernel module built for the standard Red Hat Enterprise Linux 6 kernel. KVM can run multiple,unmodified virtualized guest Windows and Linux operating systems.The KVM hypervisor in Red HatEnterprise Linux is managed with the libvirt API and tools built for libvirt, virt-manager and virsh.Virtualized guests are run as Linux processes and threads which are controlled by these modules.

Red Hat Enterprise Linux KVM hypervisors can be managed by the Red Hat Enterprise VirtualizationManager as an alternative to the virsh and virt-manager tools.

The kvm package also contains Linux kernel modules which manage devices, memory andmanagement APIs for the Hypervisor module itself.

This book covers virtualization topics for Red Hat Enterprise Linux 6. The Kernel based VirtualMachine (KVM) hypervisor is provided with Red Hat Enterprise Linux. The KVM hypervisor supportsFull virtualization.

OvercommittingThe KVM hypervisor supports overcommitting virtualized CPUs and memory. Overcommitting meansallocating more virtualized CPUs or memory than the available resources on the system. CPUovercommitting allows virtualized guests to run on fewer servers and in higher densities. Memoryovercommitting allows hosts to utilize memory and virtual memory to increase guest densities.

For more information on overcommitting with KVM, refer to Chapter 20, Overcommitting with KVM.

Chapter 1. Introduction

2

KSMKernel SamePage Merging (KSM) is used by the KVM hypervisor to allow KVM guests to shareidentical memory pages. These shared pages are usually common libraries or other identical, high-usedata. KSM allows for greater guest density of identical or similar guest operating systems by avoidingmemory duplication.

For more information on KSM, refer to Chapter 21, KSM.

1.3. libvirt and the libvirt toolsLibvirt is a hypervisor-independent virtualization API that is able to interact with the virtualizationcapabilities of a range of operating systems.

libvirt provides a common, generic and stable layer to securely manage virtualized guests on a host.libvirt provides a common interface for managing local systems and networked hosts. libvirt providesall APIs required to provision, create, modify, monitor, control, migrate and stop virtualized guestsif the hypervisor supports these operations. Although multiple hosts may be accessed with libvirtsimultaneously, the APIs are limited to single node operations.

libvirt is designed as a building block for higher level management tools and applications. libvirtfocuses on managing single hosts, with the exception of migration capabilities. libvirt provides APIs toenumerate, monitor and use the resources available on the managed node, including CPUs, memory,storage, networking and Non-Uniform Memory Access (NUMA) partitions. The management tools canbe located on separate physical machines from the host using secure protocols.

Red Hat Enterprise Linux 6 supports libvirt and included libvirt-based tools as its default method forvirtualization management.

libvirt is free software available under the GNU Lesser General Public License. The libvirt project aimsto provide a long term stable C API. The libvirt Open Source project currently supports Xen, QEmu,KVM, LXC, OpenVZ, VirtualBox, OpenNebula, and VMware ESX. The Red Hat Enterprise Linux 6libvirt package supports Xen on Red Hat Enterprise Linux 5 and KVM on Red Hat Enterprise Linux 5and Red Hat Enterprise Linux 6.

virshThe virsh command-line tool is built on the libvirt management API and operates as analternative to the graphical virt-manager application. The virsh command can be used in read-only mode by unprivileged users or, with root access, full administration functionality. The virshcommand is ideal for scripting virtualization administration.

The virsh command is included in the libvirt-client package.

virt-managervirt-manager is a graphical desktop tool for managing virtualized guests. virt-manager can beused to perform virtualization administration, virtualized guest creation, migration and configurationtasks. virt-manager allows access to graphical guest consoles. virt-manager can viewvirtualized guests, host statistics, device information and performance graphs. virt-manager canmanage the local hypervisor and remote hypervisors using the same interface and methods.

1.4. Virtualized hardware devicesVirtualization on Red Hat Linux 6 presents three distinct types of system devices to virtualized guests.The three types include:

Virtualized and emulated devices

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• Emulated software devices.

• Para-virtualized devices.

• Physically shared devices.

These hardware devices all appear as physically attached hardware devices to the virtualized guestbut the device drivers work in different ways.

1.4.1. Virtualized and emulated devicesThe KVM hypervisor implements many core devices for virtualized guests in software. These emulatedhardware devices are crucial for virtualizing operating systems. This section is provided as anintroduction to the emulated devices and emulated device drivers.

Emulated devices are virtual devices which exist entirely in software. The emulated devices do notrequire a real hardware device to back them.

Emulated drivers may use either a physical device or a virtual software device. Emulated drivers area translation layer between the guest and the Linux kernel (which manages the source device). Thedevice level instructions are completely translated by the KVM hypervisor. Any device, of the sametype, recognized by the Linux kernel may be used as the backing source device for the emulateddrivers.

Virtualized CPUs (VCPUs)A system has a number of virtual CPUs (VCPUs) relative to the number of physical processor cores.The number of virtual CPUs is finite and represents the total number of virtual CPUs that can beassigned to guest virtual machines.

Emulated graphics devicesTwo emulated graphics devices are provided. These devices can be connected to with the SPICEprotocol or with VNC.

• The ac97 device emulates a Cirrus CLGD 5446 PCI VGA card.

• The vga device emulates a dummy VGA card with Bochs VESA extensions (hardware level,including all non-standard modes).

Emulated system componentsVarious core system components are emulated to provide basic system functions.

• A Cirrus i440FX host PCI bridge.

• PIIX3 PCI to ISA bridge.

• A PS/2 mouse and keyboard.

• An EvTouch USB Graphics Tablet.

• A PCI UHCI USB controller and a virtualized USB hub.

• A PCI and ISA network adapters.

• Emulated serial ports.


4

Emulated sound devicesTwo emulated sound devices are available:

• The ac97 device emulates an Intel 82801AA AC97 Audio compatible sound card.

• The es1370 device emulates an ENSONIQ AudioPCI ES1370 sound card.

Emulated network driversThere are four emulated network drivers available for network devices:

• The e1000 driver emulates an Intel E1000 network adaptor (Intel 82540EM, 82573L, 82544GC).

• The ne2k_pci driver emulates a Novell NE2000 network adaptor.

• The pcnet driver emulates an AMD Lance Am7990 network adaptor.

• The rtl8139 driver emulates a Realtek 8139 network adaptor.

Emulated storage driversStorage devices and storage pools can use the emulated drivers to attach storage devices tovirtualized guests. Alternatively, the para-virtualized drivers can be used.

Note that the storage drivers are not storage devices. The drivers are used to attach a backing storagedevice, file or storage pool volume to a virtualized guest. The backing storage device can be anysupported type of storage device, file, or storage pool volume.

The emulated IDE driverThe KVM hypervisor provides two emulated PCI IDE interfaces. The emulated IDE driver can beused to attach any combination of up to four virtualized IDE hard disks or virtualized IDE CD-ROMdrives to each virtualized guest. The emulated IDE driver is used for virtualized CD-ROM andDVD-ROM drives.

The emulated floppy disk drive driverThe emulated floppy disk drive driver is used for creating virtualized floppy drives.

1.4.2. Para-virtualized driversPara-virtualized drivers are device drivers that increase the I/O performance of virtualized guests.

Para-virtualized drivers decrease I/O latency and increase I/O throughput to near bare-metal levels.It is recommended to use the para-virtualized drivers for virtualized guests running I/O intensiveapplications.

The para-virtualized drivers must be installed on the guest operating system. By default, the para-virtualized drivers are included in Red Hat Enterprise Linux 4.7 and newer, Red Hat Enterprise Linux5.4 and newer and Red Hat Enterprise Linux 6.0 and newer. The para-virtualized drivers must bemanually installed on Windows guests. For more information on using the para-virtualized drivers referto Chapter 11, KVM Para-virtualized Drivers.

Para-virtualized network driverThe para-virtualized network driver is a Red Hat branded virtual network device. The para-virtualizednetwork driver can be used as the driver for existing network devices or new network devices forvirtualized guests.

Physically shared devices

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Para-virtualized block driverThe para-virtualized block driver is a driver for all storage devices supported by the hypervisorattached to the virtualized guest (except for floppy disk drives, which must be emulated).

The para-virtualized clockGuests using the Time Stamp Counter (TSC) as a clock source may suffer timing issues.

KVM works around hosts that do not have a constant Time Stamp Counter by providing guests with apara-virtualized clock.

For more information on the para-virtualized clock refer to Chapter 14, KVM guest timingmanagement.

The para-virtualized serial driverThe para-virtualized serial driver (virtio-serial) is a bytestream-oriented, character stream driver. Thepara-virtualized serial driver provides a simple communication interface between the host's user spaceand the guest's user space where networking is not available or unusable.

The balloon driverThe balloon driver allows guests to express to the hypervisor how much memory they require. Theballoon driver allows the host to efficiently allocate memory to the guest and allow free memory to beallocated to other guests and processes.

Guests using the balloon driver can mark sections of the guest's RAM as not in use (balloon inflation).The hypervisor can free the memory and use the memory for other host processes or other guests onthat host.

When the guest requires the freed memory again, the hypervisor can reallocate RAM to the guest(balloon deflation).

1.4.3. Physically shared devicesCertain hardware platforms allow virtualized guests to directly access various hardware devices andcomponents. This process in virtualization is known as passthrough. Passthrough is known as deviceassignment in some of the KVM documentation and the KVM code.

PCI passthroughThe KVM hypervisor supports attaching PCI devices on the host system to virtualized guests.PCI passthrough allows guests to have exclusive access to PCI devices for a range of tasks. PCIpassthrough allows PCI devices to appear and behave as if they were physically attached to the guestoperating system.

Almost all PCI and PCI Express devices that support passthrough, except for graphics cards, can bedirectly attached to virtualized guests with PCI passthrough.

SR-IOVSR-IOV (Single Root I/O Virtualization) is a standard for a type of PCI passthrough which nativelyshares a single device to multiple guests.

SR-IOV enables a Single Root Function (for example, a single Ethernet port), to appear as multiple,separate, physical devices. A physical device with SR-IOV capabilities can be configured to appear


6

in the PCI configuration space as multiple functions, each device has its own configuration spacecomplete with Base Address Registers (BARs).

SR-IOV uses two new PCI functions:

• Virtualization-PF

• Virtualization VF

For more information on SR-IOV, refer to Chapter 13, SR-IOV.

NPIVN_Port ID Virtualization (NPIV) is a function available with some Fibre Channel devices. NPIV sharesa single physical N_Port as multiple N_Port IDs. NPIV provides similar functionality for Host BusAdaptors (HBAs) that SR-IOV provides for network interfaces. With NPIV, virtualized guests can beprovided with a virtual Fibre Channel initiator to Storage Area Networks (SANs).

NPIV can provide high density virtualized environments with enterprise-level storage solutions.

For more information on NPIV, refer to Chapter 29, N_Port ID Virtualization (NPIV).

1.5. StorageStorage for virtualized guests is abstracted from the physical storage used by the guest. Storage isattached to virtualized guests using the para-virtualized (Section 1.4.2, “Para-virtualized drivers”) oremulated block device drivers (Emulated storage drivers).

Storage poolsA storage pool is a file, directory, or storage device managed by libvirt for the purpose of providingstorage to virtualized guests. Storage pools are divided into storage volumes that store virtualizedguest images or are attached to virtualized guests as additional storage.

Storage pools can be divided up into volumes or allocated directly to a guest. Volumes of a storagepool can be allocated to virtualized guests. There are two categories of storage pool available:

Local storage poolsLocal storage pools are directly attached to the host server. Local storage pools include localdirectories, directly attached disks, and LVM volume groups on local devices.

Local storage pools are useful for development, testing and small deployments that do not requiremigration or large numbers of virtualized guests. Local storage pools are not suitable for manyproduction environments as local storage pools do not support live migration.

Networked (shared) storage poolsNetworked storage pools covers storage devices shared over a network using standard protocols.

Networked storage required for migrating guest virtualized guests between hosts. Networked storagepools are managed by libvirt.

Storage volumesStorage pools are divided into storage volumes. Storage volumes are an abstraction of physicalpartitions, LVM logical volumes, file-based disk images and other storage types handled by libvirt.

Virtualization security features

7

Storage volumes are presented to virtualized guests as local storage devices regardless of theunderlying hardware.

For more information on storage and virtualization refer to Part V, “Virtualization storage topics”.

1.6. Virtualization security features

SELinuxSELinux was developed by the US National Security Agency and others to provide Mandatory AccessControl (MAC) for Linux. All processes and files are given a type and access is limited by fine-grainedcontrols. SELinux limits an attackers abilities and works to prevent many common security exploitssuch as buffer overflow attacks and privilege escalation.

SELinux strengthens the security model of Red Hat Enterprise Linux hosts and virtualized Red HatEnterprise Linux guests. SELinux is configured and tested to work, by default, with all virtualizationtools shipped with Red Hat Enterprise Linux 6.

For more information on SELinux and virtualization, refer to Section 16.2, “SELinux and virtualization”.

sVirtsVirt is a technology included in Red Hat Enterprise Linux 6 that integrates SELinux and virtualization.sVirt applies Mandatory Access Control (MAC) to improve security when using virtualized guests. sVirtimproves security and hardens the system against bugs in the hypervisor that might be used as anattack vector for the host or to another virtualized guest.

For more information on sVirt, refer to Chapter 17, sVirt.

1.7. MigrationMigration is the term for the process of moving a virtualized guest from one host to another. Migrationcan be conducted offline (where the guest is suspended and then moved) or live (where a guest ismoved without suspending).

Migration is a key feature of virtualization as software is completely separated from hardware.Migration is useful for:

• Load balancing - guests can be moved to hosts with lower usage when a host becomes overloaded.

• Hardware failover - when hardware devices on the host start to fail, guests can be safely relocatedso the host can be powered down and repaired.

• Energy saving - guests can be redistributed to other hosts and host systems powered off to saveenergy and cut costs in low usage periods.

• Geographic migration - guests can be moved to another location for lower latency or in seriouscircumstances.

Migration only moves the virtualized guest's memory. The guest's storage is located on networkedstorage which is shared between the source host and the destination.

Shared, networked storage must be used for storing guest images. Without shared storage migrationis not possible. It is recommended to use libvirt managed storage pools for shared storage.


8

Offline migrationAn offline migration suspends the guest then moves an image of the guest's memory to the destinationhost. The guest is resumed on the destination host and then memory the guest used on the sourcehost is freed.

Live migrationLive migration is the process of migrating a running guest from one physical host to another physicalhost.

For more information on migration refer to Chapter 18, KVM live migration.

1.8. V2VVirtualized to virtualized migration, known as V2V, is supported in Red Hat Enterprise Linux 6 forcertain virtualized guests.

Red Hat Enterprise Linux 6 provides tools for converting virtualized guests from other types ofhypervisor to KVM. The virt-v2v tool converts and imports virtual machines from Xen, otherversions of KVM and VMware ESX.

For more information on using V2V, refer to Chapter 23, Migrating to KVM from other hypervisorsusing virt-v2v

Part I. Requirements and limitations

System requirements, supportrestrictions and limitationsfor virtualization with Red

Hat Enterprise Linux 6These chapters outline the system requirements, support restrictions, and limitations of virtualizationon Red Hat Enterprise Linux 6.

Chapter 2.

11

System requirementsThis chapter lists system requirements for successfully running virtualized guest operating systemswith Red Hat Enterprise Linux 6. Virtualization is available for Red Hat Enterprise Linux 6 on the Intel64 and AMD64 architecture.

The KVM hypervisor is provided with Red Hat Enterprise Linux 6.

For information on installing the virtualization packages, read Chapter 5, Installing the virtualizationpackages.

Minimum system requirements• 6GB free disk space

• 2GB of RAM.

Recommended system requirements• 6GB plus the required disk space recommended by the guest operating system per guest. For most

operating systems more than 6GB of disk space is recommended.

• One processor core or hyper-thread for each virtualized CPU and one for the hypervisor.

• 2GB of RAM plus additional RAM for virtualized guests.

KVM overcommit

KVM can overcommit physical resources for virtualized guests. Overcommitting resources meansthe total virtualized RAM and processor cores used by the guests can exceed the physical RAMand processor cores on the host. For information on safely overcommitting resources with KVMrefer to Chapter 20, Overcommitting with KVM.

KVM requirementsThe KVM hypervisor requires:

• an Intel processor with the Intel VT and the Intel 64 extensions, or

• an AMD processor with the AMD-V and the AMD64 extensions.

Refer to Section 24.3, “Verifying virtualization extensions” to determine if your processor has thevirtualization extensions.

Storage supportThe working guest storage methods are:

• files on local storage,

• physical disk partitions,

• locally connected physical LUNs,

• LVM partitions,

• NFS shared file systems,

• iSCSI,

Chapter 2. System requirements

12

• GFS2 clustered file systems, and

• Fibre Channel-based LUNs

• SRP devices (SCSI RDMA Protocol), the block export protocol used in Infiniband and 10GbEiWARP adapters.

File-based guest storage

File-based guest images should be stored in the /var/lib/libvirt/images/ folder. If youuse a different directory you must add the directory to the SELinux policy. Refer to Section 16.2,“SELinux and virtualization” for details.

Chapter 3.

13

KVM compatibilityThe KVM hypervisor requires a processor with the Intel-VT or AMD-V virtualization extensions.

Note that this list is not complete. Help us expand it by sending in a bug with anything you get working.

To verify whether your processor supports the virtualization extensions and for information onenabling the virtualization extensions if they are disabled, refer to Section 24.3, “Verifying virtualizationextensions”.

Red Hat Enterprise Linux 6.0 Servers with the kvm package are limited to 256 processor cores or less.

Supported guestsOperating system Support levelRed Hat Enterprise Linux 3 x86 Optimized with para-virtualized drivers

Red Hat Enterprise Linux 4 x86 Optimized with para-virtualized drivers

Red Hat Enterprise Linux 4 AMD64 and Intel 64

Optimized with para-virtualized drivers







Fedora 12 x86 Optimized with para-virtualized drivers

Fedora 12 AMD 64 and Intel 64 Optimized with para-virtualized drivers

Fedora 13 x86 Optimized with para-virtualized drivers

Fedora 13 AMD 64 and Intel 64 Optimized with para-virtualized drivers

Windows Server 2003 R2 32-Bit Optimized with para-virtualized drivers

Windows Server 2003 R2 64-Bit Optimized with para-virtualized drivers

Windows Server 2003 ServicePack 2 32-Bit


Windows Server 2003 ServicePack 2 64-Bit


Windows XP 32-Bit Optimized with para-virtualized drivers

Windows Vista 32-Bit Supported

Windows Vista 64-Bit Supported

Windows Server 2008 32-Bit Optimized with para-virtualized drivers

Windows Server 2008 (and R2)64-Bit


Windows 7 32-Bit Optimized with para-virtualized drivers

Windows 7 64-Bit Optimized with para-virtualized drivers

14

Chapter 4.

15

Virtualization limitationsThis chapter covers additional support and product limitations of the virtualization packages in Red HatEnterprise Linux 6.

4.1. General limitations for virtualization

Other limitationsFor the list of all other limitations and issues affecting virtualization read the Red Hat Enterprise Linux6 Release Notes. The Red Hat Enterprise Linux 6 Release Notes cover the present new features,known issues and limitations as they are updated or discovered.

Test before deploymentYou should test for the maximum anticipated load and virtualized network stress before deployingheavy I/O applications. Stress testing is important as there are performance drops caused byvirtualization with increased I/O usage.

4.2. KVM limitationsThe following limitations apply to the KVM hypervisor:

Maximum VCPUs per guestVirtualized guests support up to a maximum of 64 virtualized CPUs in Red Hat Enterprise Linux6.0.

Constant TSC bitSystems without a Constant Time Stamp Counter require additional configuration. Refer toChapter 14, KVM guest timing management for details on determining whether you have aConstant Time Stamp Counter and configuration steps for fixing any related issues.

Memory overcommitKVM supports memory overcommit and can store the memory of guests in swap. A guest will runslower if it is swapped frequently. When KSM is used, make sure that the swap size is the size ofthe overcommit ratio.

CPU overcommitIt is not recommended to have more than 10 virtual CPUs per physical processor core. Anynumber of overcommitted virtual CPUs above the number of physical processor cores may causeproblems with certain virtualized guests.

Overcommitting CPUs has some risk and can lead to instability. Refer to Chapter 20,Overcommitting with KVM for tips and recommendations on overcommitting CPUs.

Virtualized SCSI devicesSCSI emulation is limited to 16 virtualized (emulated) SCSI devices..

Virtualized IDE devicesKVM is limited to a maximum of four virtualized (emulated) IDE devices per guest.

Chapter 4. Virtualization limitations

16

Para-virtualized devicesPara-virtualized devices, which use the virtio drivers, are PCI devices. Presently, guests arelimited to a maximum of 32 PCI devices. Some PCI devices are critical for the guest to run andthese devices cannot be removed. The default, required devices are:

• the host bridge,

• the ISA bridge and usb bridge (The usb and isa bridges are the same device),

• the graphics card (using either the Cirrus or qxl driver), and

• the memory balloon device.

Out of the 32 available PCI devices for a guest 4 are not removable. This means there are only28 PCI slots available for additional devices per guest. Every para-virtualized network or blockdevice uses one slot. Each guest can use up to 28 additional devices made up of any combinationof para-virtualized network, para-virtualized disk devices, or other PCI devices using VT-d.

Migration limitationsLive migration is only possible with CPUs from the same vendor (that is, Intel to Intel or AMD toAMD only).

The No eXecution (NX) bit must be set to on or off for both CPUs for live migration.

Storage limitationsThe host should not use disk labels to identify file systems in the fstab file, the initrd file orused by the kernel command line. If less privileged users, especially virtualized guests, have writeaccess to whole partitions or LVM volumes the host system could be compromised.

Guest should not be given write access to whole disks or block devices (for example, /dev/sdb).Virtualized guests with access to block devices may be able to access other block devices on thesystem or modify volume labels which can be used to compromise the host system. Use partitions(for example, /dev/sdb1) or LVM volumes to prevent this issue.

SR-IOV limitationsSR-IOV is only supported with the following devices:

Intel® 82576NS Gigabit Ethernet Controller (igb driver)

Intel® 82576EB Gigabit Ethernet Controller (igb driver)

Neterion X3100 Series 10GbE PCIe (vxge driver)

Intel® 82599ES 10 Gigabit Ethernet Controller (ixgbe driver)

Intel® 82599EB 10 Gigabit Ethernet Controller (ixgbe driver)

PCI passthrough limitationsPCI passthrough (attaching PCI devices to guests) should work on systems with the AMD IOMMUor Intel VT-d technologies.

4.3. Application limitationsThere are aspects of virtualization which make virtualization unsuitable for certain types ofapplications.

Application limitations

17

Applications with high I/O throughput requirements should use the para-virtualized drivers for fullyvirtualized guests. Without the para-virtualized drivers certain applications may be unstable underheavy I/O loads.

The following applications should be avoided for their high I/O requirement reasons:

• kdump server

• netdump server

You should carefully evaluate databasing applications before running them on a virtualized guest.Databases generally use network and storage I/O devices intensively. These applications may not besuitable for a fully virtualized environment. Consider the para-virtualized drivers or PCI passthrough forincreased I/O performance. Refer to Chapter 11, KVM Para-virtualized Drivers for more information onthe para-virtualized drivers for fully virtualized guests. Refer to Chapter 12, PCI passthrough for moreinformation on the PCI passthrough.

Other applications and tools which heavily utilize I/O or require real-time performance should beevaluated carefully. Using full virtualization with the para-virtualized drivers (refer to Chapter 11, KVMPara-virtualized Drivers) or PCI passthrough (refer to Chapter 12, PCI passthrough) results in betterperformance with I/O intensive applications. Applications still suffer a small performance loss fromrunning in virtualized environments. The performance benefits of virtualization through consolidating tonewer and faster hardware should be evaluated against the potential application performance issuesassociated with using virtualization.

18

Part II. Installation

Virtualization installation topicsThese chapters cover setting up the host and installing virtualized guests with Red Hat EnterpriseLinux 6. It is recommended to read these chapters carefully to ensure successful installation ofvirtualized guest operating systems.

Chapter 5.

21

Installing the virtualization packagesBefore you can use virtualization, the virtualization packages must be installed on your computer.Virtualization packages can be installed either during the installation sequence or after installationusing the yum command and the Red Hat Network (RHN).

The KVM hypervisor uses the default Red Hat Enterprise Linux kernel with the kvm kernel module.

5.1. Installing KVM with a new Red Hat Enterprise LinuxinstallationThis section covers installing virtualization tools and KVM package as part of a fresh Red HatEnterprise Linux installation.

Need help installing?

The Installation Guide (available from redhat.com1) covers installing Red Hat Enterprise Linux indetail.

1. Start an interactive Red Hat Enterprise Linux installation from the Red Hat Enterprise LinuxInstallation CD-ROM, DVD or PXE.

2. You must enter a valid installation number when prompted to receive access to the virtualizationand other Advanced Platform packages.

3. Complete the other steps up to the package selection step.

1 http://www.redhat.com/docs/manuals/enterprise/

http://www.redhat.com/docs/manuals/enterprise/


Chapter 5. Installing the virtualization packages

22

Select the Virtual Host server role to install a platform for virtualized guests. Alternatively, selectthe Customize Now radio button to specify individual packages.

4. Select the Virtualization package group. This selects the KVM hypervisor, virt-manager,libvirt and virt-viewer for installation.

Installing KVM with a new Red Hat Enterprise Linux installation

23

5. Customize the packages (if required)Customize the Virtualization group if you require other virtualization packages.


24

Press the Close button then the Next button to continue the installation.

Note

You require a valid RHN virtualization entitlement to receive updates for the virtualizationpackages.

Installing KVM packages with Kickstart filesThis section describes how to use a Kickstart file to install Red Hat Enterprise Linux with the KVMhypervisor packages. Kickstart files allow for large, automated installations without a user manuallyinstalling each individual system. The steps in this section will assist you in creating and using aKickstart file to install Red Hat Enterprise Linux with the virtualization packages.

In the %packages section of your Kickstart file, append the following package group:

%packages@kvm

More information on Kickstart files can be found on Red Hat's website, redhat.com2, in the InstallationGuide.




Installing KVM packages on an existing Red Hat Enterprise Linux system

25

5.2. Installing KVM packages on an existing Red HatEnterprise Linux systemThe section describes the steps for installing the KVM hypervisor on a working Red Hat EnterpriseLinux 6 or newer system.

Adding packages to your list of Red Hat Network entitlementsThis section describes how to enable Red Hat Network (RHN) entitlements for the virtualizationpackages. You need these entitlements enabled to install and update the virtualization packages onRed Hat Enterprise Linux. You require a valid Red Hat Network account in order to install virtualizationpackages on Red Hat Enterprise Linux.

In addition, your machines must be registered with RHN. To register an unregistered installation ofRed Hat Enterprise Linux, run the rhn_register command and follow the prompts.

If you do not have a valid Red Hat subscription, visit the Red Hat online store3.

Procedure 5.1. Adding the Virtualization entitlement with RHN1. Log in to RHN4 using your RHN username and password.

2. Select the systems you want to install virtualization on.

3. In the System Properties section the present systems entitlements are listed next to theEntitlements header. Use the (Edit These Properties) link to change your entitlements.

4. Select the Virtualization checkbox.

Your system is now entitled to receive the virtualization packages. The next section covers installingthese packages.

Installing the KVM hypervisor with yumTo use virtualization on Red Hat Enterprise Linux you require the kvm package. The kvm packagecontains the KVM kernel module providing the KVM hypervisor on the default Red Hat EnterpriseLinux kernel.

To install the kvm package, run:

# yum install kvm

Now, install additional virtualization management packages.

Recommended virtualization packages:python-virtinst

Provides the virt-install command for creating virtual machines.

libvirtThe libvirt package provides the server and host side libraries for interacting with hypervisors andhost systems. The libvirt package provides the libvirtd daemon that handles the library calls,manages virtualizes guests and controls the hypervisor.

3 https://www.redhat.com/wapps/store/catalog.html

https://www.redhat.com/wapps/store/catalog.html

https://rhn.redhat.com/

https://www.redhat.com/wapps/store/catalog.html


26

libvirt-pythonThe libvirt-python package contains a module that permits applications written in the Pythonprogramming language to use the interface supplied by the libvirt API.

virt-managervirt-manager, also known as Virtual Machine Manager, provides a graphical tool foradministering virtual machines. It uses libvirt-client library as the management API.

libvirt-clientThe libvirt-client package provides the client-side APIs and libraries for accessing libvirt servers.The libvirt-client package includes the virsh command line tool to manage and control virtualizedguests and hypervisors from the command line or a special virtualization shell.

Install the other recommended virtualization packages:

# yum install virt-manager libvirt libvirt-python python-virtinst libvirt-client

Chapter 6.

27

Virtualized guest installation overviewAfter you have installed the virtualization packages on the host system you can create guest operatingsystems. This chapter describes the general processes for installing guest operating systems onvirtual machines. You can create guests using the New button in virt-manager or use the commandline interface virt-install. Both methods are covered by this chapter.

Detailed installation instructions are available for specific versions of Red Hat Enterprise Linux, otherLinux distributions, Solaris and Windows. Refer to the relevant procedure for you guest operatingsystem:

• Red Hat Enterprise Linux 5.

• Para-virtualized Red Hat Enterprise Linux 6 on Red Hat Enterprise Linux 5: Chapter 8, InstallingRed Hat Enterprise Linux 6 as a para-virtualized guest on Red Hat Enterprise Linux 5

• Red Hat Enterprise Linux 6: Chapter 7, Installing Red Hat Enterprise Linux 6 as a virtualized guest

• Microsoft Windows operating systems: Chapter 9, Installing a fully-virtualized Windows guest

6.1. Virtualized guest prerequisites and considerationsVarious factors should be considered before creating any virtualized guests. Factors include:

• Performance

• Input/output requirements and types of input/output.

• Storage.

• Networking and network infrastructure.

• Guest load and usage for processor and memory resources.

6.2. Creating guests with virt-installYou can use the virt-install command to create virtualized guests from the command line.virt-install is used either interactively or as part of a script to automate the creation of virtualmachines. Using virt-install with Kickstart files allows for unattended installation of virtualmachines.

The virt-install tool provides a number of options one can pass on the command line. To see acomplete list of options run:

$ virt-install --help

The virt-install man page also documents each command option and important variables.

qemu-img is a related command which may be used before virt-install to configure storageoptions.

An important option is the --vnc option which opens a graphical window for the guest's installation.

Example 6.1. Using virt-install to install a RHEL 5 guestThis example creates a RHEL 5 guest with the following settings:

Chapter 6. Virtualized guest installation overview

28

• Uses LVM partitioning

• Is a plain QEMU guest

• Uses virtual networking

• Boots from PXE

• Uses VNC server/viewer

# virt-install \ --network network:default \ --name rhel5support --ram=756\ --file=/var/lib/libvirt/images/rhel5support.img \ --file-size=6 --vnc --cdrom=/dev/sr0

Refer to man virt-install for more examples.

6.3. Creating guests with virt-managervirt-manager, also known as Virtual Machine Manager, is a graphical tool for creating andmanaging virtualized guests.

Procedure 6.1. Creating a virtualized guest with virt-manager1. Open virt-manager

Start virt-manager. Launch the Virtual Machine Manager application from the Applicationsmenu and System Tools submenu. Alternatively, run the virt-manager command as root.

2. Optional: Open a remote hypervisorRefer to Section 31.5, “Adding a remote connection”

Select the hypervisor and press the Connect button to connect to the remote hypervisor.

3. Create a new guestThe virt-manager window allows you to create a new virtual machine. Click the New button(Figure 6.1, “Virtual Machine Manager window”) to open the New VM wizard.

Creating guests with virt-manager

29

Figure 6.1. Virtual Machine Manager window

4. New VM wizardThe New VM wizard breaks down the guest creation process into five steps:

1. Naming the guest and choosing the installation type

2. Locating and configuring the installation media

3. Configuring memory and CPU options

4. Configuring the guest's storage

5. Configuring networking, hypervisor type, architecture, and other hardware settings

Ensure that virt-manager can access the installation media (whether locally or over thenetwork).

5. Specify name and installation typeThe guest creation process starts with the selection of a name and installation type. Virtualmachine names can have underscores (_), periods (.), and hyphens (-).


30

Figure 6.2. Step 1

Type in a virtual machine name and choose an installation type:

Local install media (ISO image or CDROM)This method uses a CD-ROM, DVD, or image of an installation disk (e.g. .iso).

Network Install (HTTP, FTP, or NFS)Network installing involves the use of a mirrored Red Hat Enterprise Linux or Fedorainstallation tree to install a guest. The installation tree must be accessible through eitherHTTP, FTP, or NFS.


31

Network Boot (PXE)This method uses a Preboot eXecution Environment (PXE) server to install the guest. Settingup a PXE server is covered in the Deployment Guide. To install via network boot, the guestmust have a routable IP address or shared network device. For information on the requirednetworking configuration for PXE installation, refer to Chapter 10, Network Configuration.

Import existing disk imageThis method allows you to create a new guest and import a disk image (containing a pre-installed, bootable operating system) to it.

Click Forward to continue.

6. Configure installationNext, configure the OS type and Version of the installation. Except for network booting, this stepalso requires further configuration (depending on your chosen installation method). When usinglocal install media or importing an existing disk image, you need to specify the location of theinstallation media or disk image.

Figure 6.3. Local install media (configuration)


32

Figure 6.4. Import existing disk image (configuration)

Important

It is recommend that you use the default directory for virtual machine images, /var/lib/libvirt/images/. If you are using a different location, make sure it is added to yourSELinux policy and relabeled before you continue with the installation. Refer to Section 16.2,“SELinux and virtualization” for details on how to do this.

When performing a network install, you need to specify the URL of the installation tree. You canalso specify the URL of any kickstart files you want to use, along with any kernel options you wantto pass during installation.


33

Figure 6.5. Network Install (configuration)


7. Configure CPU and memoryThe next step involves configuring the number of CPUs and amount of memory to allocate to thevirtual machine. The wizard shows the number of CPUs and amount of memory you can allocate;configure these settings and click Forward.


34

Figure 6.6. Configuring CPU and Memory

8. Configure storageAssign a physical storage device (Block device) or a file-based image (File). File-based imagesshould be stored in /var/lib/libvirt/images/ to satisfy default SELinux permissions.


35

Figure 6.7. Configuring virtual storage

If you chose to import an existing disk image during the first step, virt-manager will skip thisstep.

Assign sufficient space for your virtualized guest and any applications the guest requires, thenclick Forward to continue.

9. Final configurationVerify the settings of the virtual machine and click Finish when you are satisfied; doing so willcreate the guest with default networking settings, virtualization type, and architecture.


36

Figure 6.8. Verifying the configuration

If you prefer to further configure the virtual machine's hardware first, check the Customizeconfiguration before install box first before clicking Finish. Doing so will open another wizardFigure 6.9, “Virtual hardware configuration” that will allow you to add, remove, and configure thevirtual machine's hardware settings.

Installing guests with PXE

37

Figure 6.9. Virtual hardware configuration

After configuring the virtual machine's hardware, click Apply. virt-manager will then create theguest with your specified hardware settings.

This concludes the general process for creating guests with virt-manager. Chapter 6, Virtualizedguest installation overview contains step-by-step instructions to installing a variety of commonoperating systems.

6.4. Installing guests with PXEThis section covers the steps required to install guests with PXE. PXE guest installation requires ashared network device, also known as a network bridge. The procedures below covers creating abridge and the steps required to utilize the bridge for PXE installation.

1. Create a new bridgea. Create a new network script file in the /etc/sysconfig/network-scripts/ directory.

This example creates a file named ifcfg-installation which makes a bridge namedinstallation.

# cd /etc/sysconfig/network-scripts/# vim ifcfg-installationDEVICE=installation


38

TYPE=BridgeBOOTPROTO=dhcpONBOOT=yes

Warning

The line, TYPE=Bridge, is case-sensitive. It must have uppercase 'B' and lower case'ridge'.

b. Start the new bridge by restarting the network service. The ifup installation commandcan start the individual bridge but it is safer to test the entire network restarts properly.

# service network restart

c. There are no interfaces added to the new bridge yet. Use the brctl show command to viewdetails about network bridges on the system.

# brctl showbridge name bridge id STP enabled interfacesinstallation 8000.000000000000 novirbr0 8000.000000000000 yes

The virbr0 bridge is the default bridge used by libvirt for Network Address Translation(NAT) on the default Ethernet device.

2. Add an interface to the new bridgeEdit the configuration file for the interface. Add the BRIDGE parameter to the configuration file withthe name of the bridge created in the previous steps.

# Intel Corporation Gigabit Network ConnectionDEVICE=eth1BRIDGE=installationBOOTPROTO=dhcpHWADDR=00:13:20:F7:6E:8EONBOOT=yes

After editing the configuration file, restart networking or reboot.


Verify the interface is attached with the brctl show command:

# brctl showbridge name bridge id STP enabled interfacesinstallation 8000.001320f76e8e no eth1virbr0 8000.000000000000 yes

3. Security configurationConfigure iptables to allow all traffic to be forwarded across the bridge.

# iptables -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT# service iptables save


39

# service iptables restart

Disable iptables on bridges

Alternatively, prevent bridged traffic from being processed by iptables rules. In /etc/sysctl.conf append the following lines:

net.bridge.bridge-nf-call-ip6tables = 0net.bridge.bridge-nf-call-iptables = 0net.bridge.bridge-nf-call-arptables = 0

Reload the kernel parameters configured with sysctl.

# sysctl -p /etc/sysctl.conf

4. Restart libvirt before the installationRestart the libvirt daemon.

# service libvirtd reload

The bridge is configured, you can now begin an installation.

PXE installation with virt-installFor virt-install append the --network=bridge:installation installation parameter whereinstallation is the name of your bridge. For PXE installations use the --pxe parameter.

Example 6.2. PXE installation with virt-install

# virt-install --hvm --connect qemu:///system \ --network=bridge:installation --pxe\ --name EL10 --ram=756 \ --vcpus=4 --os-type=linux --os-variant=rhel5 --file=/var/lib/libvirt/images/EL10.img \

PXE installation with virt-managerThe steps below are the steps that vary from the standard virt-manager installation procedures.

1. Select PXESelect PXE as the installation method.


40

2. Select the bridgeSelect Shared physical device and select the bridge created in the previous procedure.


41

3. Start the installationThe installation is ready to start.


42

A DHCP request is sent and if a valid PXE server is found the guest installation processes will start.

Chapter 7.

43

Installing Red Hat Enterprise Linux 6 asa virtualized guestThis Chapter covers how to install Red Hat Enterprise Linux 6 as a fully virtualized guest on Red HatEnterprise Linux 6.

This procedure assumes that the KVM hypervisor and all other required packages are installed andthe host is configured for virtualization. For more information on installing the virtualization pacakges,refer to Chapter 5, Installing the virtualization packages.

7.1. Creating a Red Hat Enterprise Linux 6 guest with localinstallation mediaThis procedure covers creating a virtualized Red Hat Enterprise Linux 6 guest with a locally storedinstallation DVD or DVD image. DVD images are available from rhn.redhat.com1 for Red HatEnterprise Linux 6.

Procedure 7.1. Creating a Red Hat Enterprise Linux 6 guest with virt-manager1. Optional: Preparation

Prepare the storage environment for the virtualized guest. For more information on preparingstorage, refer to Part V, “Virtualization storage topics”.

Note

Various storage types may be used for storing virtualized guests. However, for a guest to beable to use migration features the guest must be created on networked storage.

Red Hat Enterprise Linux 6 requires at least 1GB of storage space. However, Red Hatrecommends at least 5GB of storage space for a Red Hat Enterprise Linux 6 installation and forthe procedures in this guide.

2. Open virt-manager and start the wizardOpen virt-manager by executing the virt-manager command as root or opening Applications ->System Tools -> Virtual Machine Manager.

1 http://www.rhn.redhat.com

http://www.rhn.redhat.com

http://www.rhn.redhat.com

Chapter 7. Installing Red Hat Enterprise Linux 6 as a virtualized guest

44

Figure 7.1. The main virt-manager window

Press the create new virtualized guest button (see figure Figure 7.2, “The create newvirtualized guest button”) to start the new virtualized guest wizard.

Figure 7.2. The create new virtualized guest button

The Create a new virtual machine window opens.

3. Name the virtualized guestGuest names can contain letters, numbers and the following characters: '_', '.' and '-'. Guestnames must be unique for migration.

Choose the Local install media (ISO image or CDROM) radio button.

Creating a Red Hat Enterprise Linux 6 guest with local installation media

45

Figure 7.3. The Create a new virtual machine window - Step 1

Press Forward to continue.

4. Select the installation mediaSelect the installation ISO image location or a DVD drive with the installation disc inside. Thisexample uses an ISO file image of the Red Hat Enterprise Linux 6.0 installation DVD image.


46

Figure 7.4. The Locate ISO media volume window

Image files and SELinux

For ISO image files and guest storage images, the recommended directory to use is the/var/lib/libvirt/images/ directory. Any other location may require additionalconfiguration for SELinux, refer to Section 16.2, “SELinux and virtualization” for details.

Select the operating system type and version which match the installation media you haveselected.


47



5. Set RAM and virtual CPUsChoose appropriate values for the virtualized CPUs and RAM allocation. These values affect thehost's and guest's performance. Memory and virtualized CPUs can be overcommitted, for moreinformation on overcommitting refer to Chapter 20, Overcommitting with KVM.

Virtualized guests require sufficient physical memory (RAM) to run efficiently and effectively. RedHat supports a minimum of 512MB of RAM for a virtualized guest. Red Hat recommends at least1024MB of RAM for each logical core.

Assign sufficient virtual CPUs for the virtualized guest. If the guest runs a multithreadedapplication, assign the number of virtualized CPUs the guest will require to run efficiently.

You cannot assign more virtual CPUs than there are physical processors (or hyper-threads)available on the host system. The number of virtual CPUs available is noted in the Up to Xavailable field.


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6. StorageEnable and assign storage for the Red Hat Enterprise Linux 6 guest. Assign at least 5GB for adesktop installation or at least 1GB for a minimal installation.

Migration

Live and offline migrations require guests to be installed on shared network storage. Forinformation on setting up shared storage for guests refer to Part V, “Virtualization storagetopics”.

a. With the default local storageSelect the Create a disk image on the computer's hard drive radio button to create afile-based image in the default storage pool, the /var/lib/libvirt/images/ directory.Enter the size of the disk image to be created. If the Allocate entire disk now check box isselected, a disk image of the size specified will be created immediately. If not, the disk imagewill grow as it becomes filled.


49


b. With a storage poolSelect Select managed or other existing storage to use a storage pool.


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Figure 7.8. The Locate or create storage volume window

i. Press the browse button to open the storage pool browser.

ii. Select a storage pool from the Storage Pools list.

iii. Optional: Press the New Volume button to create a new storage volume. Enter the nameof the new storage volume.

iv. Press the Choose Volume button to select the volume for the virtualized guest.


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7. Verify and finishVerify there were no errors made during the wizard and everything appears as expected.

Select the Customize configuration before install check box to change the guest's storage ornetwork devices, to use the para-virtualized drivers or, to add additional devices.

Press the Advanced options down arrow to inspect and modify advanced options. For a standardRed Hat Enterprise Linux 6 none of these options require modification.


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Press Finish to continue into the Red Hat Enterprise Linux installation sequence. For moreinformation on installing Red Hat Enterprise Linux 6 refer to the Red Hat Enterprise Linux 6Installation Guide.

A Red Hat Enterprise Linux 6 guest is now created from a an ISO installation disc image.

Creating a Red Hat Enterprise Linux 6 guest with a network installation tree

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7.2. Creating a Red Hat Enterprise Linux 6 guest with anetwork installation tree



Note





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Choose the installation method from the list of radio buttons.

Creating a Red Hat Enterprise Linux 6 guest with PXE

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7.3. Creating a Red Hat Enterprise Linux 6 guest with PXE



Note




56







Creating a Red Hat Enterprise Linux 6 guest with PXE

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Choose the installation method from the list of radio buttons.



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Chapter 8.

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Installing Red Hat Enterprise Linux 6as a para-virtualized guest on Red HatEnterprise Linux 5This section describes how to install Red Hat Enterprise Linux 6 as a para-virtualized guest on RedHat Enterprise Linux 5. Para-virtualization is only available for Red Hat Enterprise Linux 5 hosts. RedHat Enterprise Linux 6 uses the PV-opts features of the Linux kernel to appear as a compatible Xenpara-virtualized guest.

Important note on para-virtualization

Para-virtualization only works with the Xen hypervisor. Para-virtualization does not work with theKVM hypervisor. This procedure is for Red Hat Enterprise Linux 5.4 or newer.

8.1. Using virt-installThis section covers creating a para-virtualized Red Hat Enterprise Linux 6 guest on a Red HatEnterprise Linux 5 host using the virt-install command. For instructions on virt-manager,refer to the procedure in Section 8.2, “Using virt-manager”.

This method installs Red Hat Enterprise Linux 6 from a remote server hosting the network installationtree. The installation instructions presented in this section are similar to installing from the minimalinstallation live CD-ROM.

Automating with virt-install

Guests can be created with the command line virt-install tool. The --vnc option shows thegraphical installation. The name of the guest in the example is rhel6PV, the disk image file isrhel6PV.img and a local mirror of the Red Hat Enterprise Linux 6 installation tree is http://example.com/installation_tree/RHEL6-x86/. Replace those values with values for yoursystem and network.

# virt-install --name rhel6PV \--disk /var/lib/libvirt/images/rhel6PV.img,size=5 \--vnc --paravirt --vcpus=2 --ram=1024 \-location=http://example.com/installation_tree/RHEL6-x86/

Red Hat Enterprise Linux can be installed without a graphical interface or manual input. Use aKickstart file to automate the installation process. This example extends the previous examplewith a Kickstart file, located at http://example.com/kickstart/ks.cfg, to fully automatethe installation.

# virt-install --name rhel6PV \--disk /var/lib/libvirt/images/rhel6PV.img,size=5 \--nographics --paravirt --vcpus=2 --ram=1024 \-location=http://example.com/installation_tree/RHEL6-x86/ \-x "ks=http://example.com/kickstart/ks.cfg"

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The graphical console opens showing the initial boot phase of the guest:

After your guest has completed its initial boot, the standard installation process for Red Hat EnterpriseLinux 6 starts. For most systems the default answers are acceptable.

Refer to the Red Hat Enterprise Linux 6 Installation Guide for more information on installing Red HatEnterprise Linux 6.

8.2. Using virt-manager

Procedure 8.1. Creating a para-virtualized Red Hat Enterprise Linux 6 guest with virt-manager1. Open virt-manager

Start virt-manager. Launch the Virtual Machine Manager application from the Applicationsmenu and System Tools submenu. Alternatively, run the virt-manager command as root.

2. Select the hypervisorSelect the hypervisor. Note that presently the KVM hypervisor is named qemu.

Connect to a hypervisor if you have not already done so. Open the File menu and select the AddConnection... option. Refer to Section 31.5, “Adding a remote connection”.

Once a hypervisor connection is selected the New button becomes available. Press the Newbutton.

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3. Start the new virtual machine wizardPressing the New button starts the virtual machine creation wizard.


4. Name the virtual machineProvide a name for your virtualized guest. The following punctuation and whitespace charactersare permitted for '_', '.' and '-' characters.


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5. Choose a virtualization methodSelect Xen para-virtualized as the virtualization method.

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6. Select the installation methodRed Hat Enterprise Linux can be installed using one of the following methods:

• local install media, either an ISO image or physical optical media.

• Select Network install tree if you have the installation tree for Red Hat Enterprise Linux hostedsomewhere on your network via HTTP, FTP or NFS.

• PXE can be used if you have a PXE server configured for booting Red Hat Enterprise Linuxinstallation media. Configuring a sever to PXE boot a Red Hat Enterprise Linux installation isnot covered by this guide. However, most of the installation steps are the same after the mediaboots.

Set OS Type to Linux and OS Variant to Red Hat Enterprise Linux 5 as shown in thescreenshot.


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7. Locate installation mediaSelect ISO image location or CD-ROM or DVD device. This example uses an ISO file image ofthe Red Hat Enterprise Linux installation DVD.

a. Press the Browse button.

b. Search to the location of the ISO file and select the ISO image. Press Open to confirm yourselection.

c. The file is selected and ready to install.

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Image files and SELinux

For ISO image files and guest storage images it is recommended to use the /var/lib/libvirt/images/ directory. Any other location may require additional configuration forSELinux, refer to Section 16.2, “SELinux and virtualization” for details.

8. Storage setupAssign a physical storage device (Block device) or a file-based image (File). File-based imagesshould be stored in the /var/lib/libvirt/images/ directory to satisfy default SELinuxpermissions. Assign sufficient space for your virtualized guest and any applications the guestrequires.


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Migration

Live and offline migrations require guests to be installed on shared network storage. Forinformation on setting up shared storage for guests refer to Part V, “Virtualization storagetopics”.

9. Network setupSelect either Virtual network or Shared physical device.

The virtual network option uses Network Address Translation (NAT) to share the default networkdevice with the virtualized guest. Use the virtual network option for wireless networks.

The shared physical device option uses a network bond to give the virtualized guest full access toa network device.

Using virt-manager

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10. Memory and CPU allocationThe Memory and CPU Allocation window displays. Choose appropriate values for the virtualizedCPUs and RAM allocation. These values affect the host's and guest's performance.

Virtualized guests require sufficient physical memory (RAM) to run efficiently and effectively.Choose a memory value which suits your guest operating system and application requirements.Remember, guests use physical RAM. Running too many guests or leaving insufficient memoryfor the host system results in significant usage of virtual memory and swapping. Virtual memory issignificantly slower which causes degraded system performance and responsiveness. Ensure youallocate sufficient memory for all guests and the host to operate effectively.

Assign sufficient virtual CPUs for the virtualized guest. If the guest runs a multithreadedapplication, assign the number of virtualized CPUs the guest will require to run efficiently. Donot assign more virtual CPUs than there are physical processors (or hyper-threads) available onthe host system. It is possible to over allocate virtual processors, however, over allocating hasa significant, negative effect on guest and host performance due to processor context switchingoverheads.


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11. Verify and start guest installationVerify the configuration.

Using virt-manager

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Press Finish to start the guest installation procedure.

12. Installing Red Hat Enterprise LinuxComplete the Red Hat Enterprise Linux installation sequence. The installation sequence iscovered by the Red Hat Enterprise Linux 6 Installation Guide. Refer to Red Hat Documentation1

for the Red Hat Enterprise Linux 6 Installation Guide.

http://redhat.com/docs

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Chapter 9.

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Installing a fully-virtualized WindowsguestRed Hat Enterprise Linux 6 supports the installation of any Microsoft Windows operating systemas a fully virtualized guest. This chapter describes how to create a fully virtualized guest using thecommand-line (virt-install), launch the operating system's installer inside the guest, and accessthe installer through virt-viewer.

To install a Windows operating system on the guest, use the virt-viewer tool. This tool allowsyou to display the graphical console of a virtual machine (via the VNC protocol). In doing so, virt-viewer allows you to install a fully virtualized guest's operating system through that operatingsystem's installer (e.g. the Windows XP installer).

Installing a Windows operating system involves two major steps:

1. Creating the guest (using either virt-install or virt-manager)

2. Installing the Windows operating system on the guest (through virt-viewer)

Note that this chapter does not describe how to install a Windows operating system on a fully-virtualized guest. Rather, it only covers how to create the guest and launch the installer within theguest. For information on how to install a Windows operating system, refer to the relevant Microsoftinstallation documentation.

9.1. Using virt-install to create a guestThe virt-install command allows you to create a fully-virtualized guest from a terminal, i.e.without a GUI. If you prefer to use a GUI instead, refer to Section 6.3, “Creating guests with virt-manager” for instructions on how to use virt-manager.

Important

Before creating the guest, consider first if the guest needs to use KVM Windows para-virtualizeddrivers. If it does, keep in mind that you can do so during or after installing the Windows operatingsystem on the guest. For more information about para-virtualized drivers, refer to Chapter 11,KVM Para-virtualized Drivers.

For instructions on how to install KVM para-virtualized drivers, refer to Section 11.2, “Installing theKVM Windows para-virtualized drivers”.

It is possible to create a fully-virtualized guest with only a single command. To do so, simply run thefollowing program (replace the values accordingly):

# virt-install \ --name=guest-name \ --network network=default \ --disk path=path-to-disk \ --disk size=disk-size \ --cdrom=path-to-install-disk \ --vnc --ram=1024

The path-to-disk must be a device (e.g. /dev/sda3) or image file (/var/lib/libvirt/images/name.img). It must also have enough free space to support the disk-size.

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Important

All image files should be stored in /var/lib/libvirt/images/. Other directory locationsfor file-based images are prohibited by SELinux. If you run SELinux in enforcing mode, refer toSection 16.2, “SELinux and virtualization” for more information on installing guests.

You can also run virt-install interactively. To do so, use the --prompt command, as in:

# virt-install --prompt

Once the fully-virtualized guest is created, virt-viewer will launch the guest and run the operatingsystem's installer. Refer to to the relevant Microsoft installation documentation for instructions on howto install the operating system.

Important

If you are installing Windows 2003, you will need to select a different computer type beforeinstalling the operating system. As soon as virt-viewer launches, press F5 and refer toSection 9.2, “Installing Windows 2003” for further instructions before proceeding.

9.2. Installing Windows 2003Windows 2003 requires a specific computer type in order to install properly on a fully-virtualized guest.This needs to be specified at the beginning of the installation process.

As soon as virt-viewer launches and boots the installer, press F5. If you do not press F5 at theright time you will need to restart the installation. Pressing F5 allows you to select a different HAL orComputer Type.

Figure 9.1. Selecting a different HAL

Choose Standard PC as the Computer Type. Then, press Enter to continue with the installationprocess.

Part III. Configuration

Configuring virtualization inRed Hat Enterprise Linux 6

These chapters cover configuration procedures for various advanced virtualization tasks. These tasksinclude adding network and storage devices, enhancing security, improving performance, and usingthe para-virtualized drivers on fully virtualized guests.

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Network ConfigurationThis page provides an introduction to the common networking configurations used by libvirt basedapplications. For additional information consult the libvirt network architecture documentation: http://libvirt.org/intro.html.

Red Hat Enterprise Linux 6 supports the following networking setups for virtualization:

• virtual networks using Network Address Translation (NAT)

• directly allocated physical devices using PCI passthrough or SR-IOV.

• bridged networks

You must enable NAT, network bridging or directly share a physical device to allow external hostsaccess to network services on virtualized guests.

10.1. Network Address Translation (NAT) with libvirtOne of the most common methods for sharing network connections is to use Network AddressTranslation (NAT) forwarding (also know as virtual networks).

Host configurationEvery standard libvirt installation provides NAT based connectivity to virtual machines out of thebox. This is the so called 'default virtual network'. Verify that it is available with the virsh net-list--all command.

# virsh net-list --allName State Autostart -----------------------------------------default active yes

If it is missing, the example XML configuration file can be reloaded and activated:

# virsh net-define /usr/share/libvirt/networks/default.xml

The default network is defined from /usr/share/libvirt/networks/default.xml

Mark the default network to automatically start:

# virsh net-autostart defaultNetwork default marked as autostarted

Start the default network:

# virsh net-start defaultNetwork default started

Once the libvirt default network is running, you will see an isolated bridge device. This device doesnot have any physical interfaces added. The new device uses NAT and IP forwarding to connect tooutside world. Do not add new interfaces.

# brctl showbridge name bridge id STP enabled interfacesvirbr0 8000.000000000000 yes

http://libvirt.org/intro.html

http://libvirt.org/intro.html

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libvirt adds iptables rules which allow traffic to and from guests attached to the virbr0 devicein the INPUT, FORWARD, OUTPUT and POSTROUTING chains. libvirt then attempts to enable theip_forward parameter. Some other applications may disable ip_forward, so the best option is toadd the following to /etc/sysctl.conf.

net.ipv4.ip_forward = 1

Guest configurationOnce the host configuration is complete, a guest can be connected to the virtual network based onits name. To connect a guest to the 'default' virtual network, the following could be used in the XMLconfiguration file (such as /etc/libvirtd/qemu/myguest.xml) for the guest:

<interface type='network'> <source network='default'/></interface>

Note

Defining a MAC address is optional. A MAC address is automatically generated if omitted.Manually setting the MAC address may be useful to maintain consistency or easy referencethroughout your environment, or to avoid the very small chance of a conflict.

<interface type='network'> <source network='default'/> <mac address='00:16:3e:1a:b3:4a'/></interface>

10.2. Bridged networking with libvirtBridged networking (also known as physical device sharing) is used for dedicating a physical deviceto a virtual machine. Bridging is often used for more advanced setups and on servers with multiplenetwork interfaces.

Disable NetworkManagerNetworkManager does not support bridging. NetworkManager must be disabled to use networking withthe network scripts (located in the /etc/sysconfig/network-scripts/ directory).

# chkconfig NetworkManager off# chkconfig network on# service NetworkManager stop# service network start

Note

Instead of turning off NetworkManager, add "NM_CONTROLLED=no" to the ifcfg-* scripts usedin the examples.

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Creating the bridgeCreate or edit the following two network configuration files. These steps can be repeated (with differentnames) for additional network bridges.

1. Change to the network scripts directoryChange to the /etc/sysconfig/network-scripts directory:

# cd /etc/sysconfig/network-scripts

2. Modify a network interface to make a bridgeEdit the network script for the network device you are adding to the bridge. In this example,/etc/sysconfig/network-scripts/ifcfg-eth0 is used. This file defines eth0, thephysical network interface which is set as part of a bridge:

DEVICE=eth0# change the hardware address to match the hardware address your NIC usesHWADDR=00:16:76:D6:C9:45ONBOOT=yesBRIDGE=br0

Tip

You can configure the device's Maximum Transfer Unit (MTU) by appending an MTU variableto the end of the configuration file.

MTU=9000

3. Create the bridge scriptCreate a new network script in the /etc/sysconfig/network-scripts directory calledifcfg-br0 or similar. The br0 is the name of the bridge, this can be anything as long as thename of the file is the same as the DEVICE parameter, and that it matches the bridge name usedin step 2.

DEVICE=br0TYPE=BridgeBOOTPROTO=dhcpONBOOT=yesDELAY=0

Warning

The line, TYPE=Bridge, is case-sensitive. It must have uppercase 'B' and lower case 'ridge'.

4. Restart the networkAfter configuring, restart networking or reboot.


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5. Configure iptablesConfigure iptables to allow all traffic to be forwarded across the bridge.

# iptables -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT# service iptables save# service iptables restart

Disable iptables on bridges

Alternatively, prevent bridged traffic from being processed by iptables rules. In /etc/sysctl.conf append the following lines:

net.bridge.bridge-nf-call-ip6tables = 0net.bridge.bridge-nf-call-iptables = 0net.bridge.bridge-nf-call-arptables = 0

Reload the kernel parameters configured with sysctl.

# sysctl -p /etc/sysctl.conf

6. Restart the libvirt serviceRestart the libvirt service with the service command.

# service libvirtd reload

7. Verify the bridgeVerify the new bridge is available with the bridge control command (brctl).

# brctl showbridge name bridge id STP enabled interfacesvirbr0 8000.000000000000 yesbr0 8000.000e0cb30550 no eth0

A "Shared physical device" is now available through virt-manager and libvirt, which guests can beattached and have full network access.

Note, the bridge is completely independent of the virbr0 bridge. Do not attempt to attach a physicaldevice to virbr0. The virbr0 bridge is only for Network Address Translation (NAT) connectivity.

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KVM Para-virtualized DriversPara-virtualized drivers are available for virtualized Windows guests running on KVM hosts. Thesepara-virtualized drivers are included in the virtio package. The virtio package supports block (storage)devices and network interface controllers.

Para-virtualized drivers enhance the performance of fully virtualized guests. With the para-virtualizeddrivers guest I/O latency decreases and throughput increases to near bare-metal levels. It isrecommended to use the para-virtualized drivers for fully virtualized guests running I/O heavy tasksand applications.

The KVM para-virtualized drivers are automatically loaded and installed on the following:

• Red Hat Enterprise Linux 3.9 and newer



• Red Hat Enterprise Linux 6 and newer

• Some versions of Linux based on the 2.6.27 kernel or newer kernel versions.

Versions of Red Hat Enterprise Linux in the list above detect and install the drivers, additionalinstallation steps are not required.

Note

PCI devices are limited by the virtualized system architecture. Out of the 32 available PCI devicesfor a guest, 4 are not removable. This means there are up to 28 free PCI slots available foradditional devices per guest. Each PCI device in a guest can have up to 8 functions.

The following Microsoft Windows versions are expected to function normally using KVM para-virtualized drivers:

• Windows XP (32-bit only)

• Windows Server 2003 (32-bit and 64-bit versions)

• Windows Server 2008 (32-bit and 64-bit versions)

• Windows 7 (32-bit and 64-bit versions)

11.1. Using the para-virtualized drivers with Red HatEnterprise Linux 3.9 guestsPara-virtualized drivers for Red Hat Enterprise Linux 3.9 consist of five kernel modules: virtio,virtio_blk, virtio_net, virtio_pci and virtio_ring. All five modules must be loaded touse both the para-virtualized block and network devices drivers.

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Note

To use the network device driver only, load the virtio, virtio_net and virtio_pcimodules. To use the block device driver only, load the virtio, virtio_ring, virtio_blkand virtio_pci modules.

Modified initrd files

The virtio package modifies the initrd RAM disk file in the /boot directory. The original initrd fileis saved to /boot/initrd- kernel-version .img.virtio.orig. The original initrd file isreplaced with a new initrd RAM disk containing the virtio driver modules. The initrd RAM diskis modified to allow the guest to boot from a storage device using the para-virtualized drivers.To use a different initrd file, you must ensure that drivers are loaded with the sysinit script(Loading the para-virtualized drivers with the sysinit script) or when creating new initrd RAM disk(Adding the para-virtualized drivers to the initrd RAM disk).

Loading the para-virtualized drivers with the sysinit scriptThis procedure covers loading the para-virtualized driver modules during the boot sequence on a RedHat Enterprise Linux 3.9 or newer guest with the sysinit script. Note that the guest cannot use thepara-virtualized drivers for the default boot disk if the modules are loaded with the sysinit script.

The drivers must be loaded in the following order:

1. virtio

2. virtio_ring

3. virtio_blk

4. virtio_net

5. virtio_pci

Only order of virtio_net and virtio_blk can be change. If the drivers are loaded in a differentorder, drivers will not work.

Configure the modules to . Locate the following section of the /etc/rc.d/rc.sysinit file.

if [ -f /etc/rc.modules ]; then /etc/rc.modulesfi

Append the following lines after that section:

if [ -f /etc/rc.modules ]; then /etc/rc.modulesfi

modprobe virtiomodprobe virtio_ring # Comment this out if you do not need block drivermodprobe virtio_blk # Comment this out if you do not need block drivermodprobe virtio_net # Comment this out if you do not need net driver

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modprobe virtio_pci

Reboot the guest to load the kernel modules.

Adding the para-virtualized drivers to the initrd RAM diskThis procedure covers loading the para-virtualized driver modules with the kernel on a Red HatEnterprise Linux 3.9 or newer guest by including the modules in the initrd RAM disk. The mkinitrd toolconfigures the initrd RAM disk to load the the modules. Specify the additional modules with the --with parameter for the mkinitrd command. Append following set of parameters, in the exact order,when using the mkinitrd command to create a custom initrd RAM disk:

--with virtio --with virtio_ring --with virtio_blk --with virtio_net --with virtio_pci

AMD64 and Intel 64 issuesUse the x86_64 version of the virtio package for AMD64 systems.

Use the ia32e version of the virtio package for Intel 64 systems. Using the x86_64 version of thevirtio may cause a 'Unresolved symbol' error during the boot sequence on Intel 64 systems.

Network performance issuesIf you experience low performance with the para-virtualized network drivers, verify the setting for theGSO and TSO features on the host system. The para-virtualized network drivers require that the GSOand TSO options are disabled for optimal performance.

Verify the status of the GSO and TSO settings, use the command on the host (replacing interfacewith the network interface used by the guest):

# ethtool -k interface

Disable the GSO and TSO options with the following commands on the host:

# ethtool -K interface gso off# ethtool -K interface tso off

Para-virtualized driver swap partition issueAfter activating the para-virtualized block device driver the swap partition may not be available. Thisissue is may be caused by a change in disk device name. To fix this issue, open the /etc/fstab fileand locate the lines containing swap partitions, for example:

/dev/hda3 swap swap defaults 0 0

The para-virtualized drivers use the /dev/vd* naming convention, not the /dev/hd* namingconvention. To resolve this issue modify the incorrect swap entries in the /etc/fstab file to use the/dev/vd* convention, for the example above:

/dev/vda3 swap swap defaults 0 0

Save the changes and reboot the virtualized guest. The guest should now correctly have swappartitions.


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11.2. Installing the KVM Windows para-virtualized driversThis section covers the installation process for the KVM Windows para-virtualized drivers. The KVMpara-virtualized drivers can be loaded during the Windows installation or installed after the guest isinstalled.

You can install the para-virtualized drivers on your guest by one of the following methods:• hosting the installation files on a network accessible to the guest,

• using a virtualized CD-ROM device of the driver installation disk .iso file, or

• using a virtualized floppy device to install the drivers during boot time (for Windows guests).

This guide describes installation from the para-virtualized installer disk as a virtualized CD-ROMdevice.

1. Download the driversThe virtio-win package contains the para-virtualized block and network drivers for all supportedWindows guests.

Download the virtio-win package with the yum command.

# yum install virtio-win

The drivers are also from Microsoft (windowsservercatalog.com1). Note that the Red HatEnterprise Virtualization Hypervisor and Red Hat Enterprise Linux are created on the samecode base so the drivers for the same version (for example, Red Hat Enterprise VirtualizationHypervisor 2.2 and Red Hat Enterprise Linux 5.5) are supported for both environments.

The virtio-win package installs a CD-ROM image, virtio-win.iso, in the /usr/share/virtio-win/ directory.

2. Install the para-virtualized driversIt is recommended to install the drivers on the guest before attaching or modifying a device to usethe para-virtualized drivers.

For block devices storing root file systems or other block devices required for booting the guest,the drivers must be installed before the device is modified. If the drivers are not installed on theguest and the driver is set to the virtio driver the guest will not boot.

11.2.1. Installing the drivers on an installed Windows guestThis procedure covers installing the para-virtualized drivers with a virtualized CD-ROM after Windowsis installed.

Follow Procedure 11.1, “Installing from the driver CD-ROM image with virt-manager” to add a CD-ROM image with virt-manager and then install the drivers.

Procedure 11.1. Installing from the driver CD-ROM image with virt-manager1. Open virt-manager and the guest

Open virt-manager, select your virtualized guest from the list by double clicking the guestname.

2. Open the hardware windowClick the blue Information button at the top to view guest details. Then click the Add Hardwarebutton at the bottom of the window.

http://www.windowsservercatalog.com/results.aspx?text=Red+Hat&bCatID=1282&avc=10&ava=0&OR=5&=Go&chtext=&cstext=&csttext=&chbtext=

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3. Select the device typeThis opens a wizard for adding the new device. Select Storage from the dropdown menu.


84

Click the Forward button to proceed.

4. Select the ISO fileSelect Select managed or other existing storage and set the file location of the para-virtualizeddrivers .iso image file. The default location for the latest version of the drivers is /usr/share/virtio-win/virtio-win.iso.

Change the Device type to IDE cdrom and click the Forward button to proceed.


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5. Finish adding virtual hardwarePress the Finish button to complete the wizard.


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6. RebootReboot or start the guest to begin using the driver disc. Virtualized IDE devices require a restart tofor the guest to recognize the new device.

Once the CD-ROM with the drivers is attached and the guest has started, proceed withProcedure 11.2, “Windows installation”.

Procedure 11.2. Windows installation1. Open My Computer

On the Windows guest, open My Computer and select the CD-ROM drive.


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2. Select the correct installation filesThere are four files available on the disc. Select the drivers you require for your guest'sarchitecture:

• the para-virtualized block device driver (RHEV-Block.msi for 32-bit guests or RHEV-Block64.msi for 64-bit guests),

• the para-virtualized network device driver (RHEV-Network.msi for 32-bit guests or RHEV-Block64.msi for 64-bit guests),

• or both the block and network device drivers.

Double click the installation files to install the drivers.

3. Install the block device drivera. Start the block device driver installation

Double click RHEV-Block.msi or RHEV-Block64.msi.


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Press Install to continue.

b. Confirm the exceptionWindows may prompt for a security exception.

Press Yes if it is correct.


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c. Finish

Press Finish to complete the installation.

4. Install the network device drivera. Start the network device driver installation

Double click RHEV-Network.msi or RHEV-Network64.msi.


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Press Next to continue.

b. Performance settingThis screen configures advanced TCP settings for the network driver. TCP timestamps andTCP window scaling can be enabled or disabled. The default is, 1, for window scaling to beenabled.

TCP window scaling is covered by IETF RFC 13232. The RFC defines a method of increasingthe receive window size to a size greater than the default maximum of 65,535 bytes up to anew maximum of 1 gigabyte (1,073,741,824 bytes). TCP window scaling allows networks totransfer at closer to theoretical network bandwidth limits. Larger receive windows may not besupported by some networking hardware or operating systems.

TCP timestamps are also defined by IETF RFC 13233. TCP timestamps are used to bettercalculate Return Travel Time estimates by embedding timing information is embedded inpackets. TCP timestamps help the system to adapt to changing traffic levels and avoidcongestion issues on busy networks.

Value Action0 Disable TCP timestamps and window scaling.

1 Enable TCP window scaling.

2 Enable TCP timestamps.

3 Enable TCP timestamps and window scaling.

http://tools.ietf.org/html/rfc1323

http://tools.ietf.org/html/rfc1323


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Press Next to continue.

c. Confirm the exceptionWindows may prompt for a security exception.

Press Yes if it is correct.


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d. Finish

Press Finish to complete the installation.

5. RebootReboot the guest to complete the driver installation.

Change an existing device to use the para-virtualized drivers (Section 11.3, “Using KVM para-virtualized drivers for existing devices”) or install a new device using the para-virtualized drivers(Section 11.4, “Using KVM para-virtualized drivers for new devices”).

11.2.2. Installing drivers during the Windows installationThis procedure covers installing the para-virtualized drivers during a Windows installation.

This method allows a Windows guest to use the para-virtualized (virtio) drivers for the defaultstorage device.

1. Install the virtio-win package:

# yum install virtio-win

Creating guests

Create the guest, as normal, without starting the guest. Follow one of the procedures below.

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2. Creating the guest with virshThis method attaches the para-virtualized driver floppy disk to a Windows guest before theinstallation.

If the guest is created from an XML definition file with virsh use the virsh define commandnot the virsh create command.

a. Create, but do not start, the guest. Refer to Chapter 30, Managing guests with virsh fordetails on creating guests with the virsh command.

b. Add the driver disk as a virtualized floppy disk with the virsh command. This example canbe copied and used if there are no other virtualized floppy devices attached to the virtualizedguest.

# virsh attach-disk guest1 /usr/share/virtio-win/virtio-drivers.vfd fda --type floppy

3. Creating the guest with virt-managera. At the final step of the virt-manager guest creation wizard, check the Customize

configuration before install checkbox.


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Press the Finish button to continue.

b. Add the new deviceSelect Storage from the Hardware type list. Click Forward to continue.


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c. Select the driver diskSelect Select managed or existing storage.

Set the location to /usr/share/virtio-win/virtio-drivers.vfd.

Change Device type to Floppy disk.


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Press the Forward button to continue.

d. Confirm the new deviceClick the Finish button to confirm the device setup and add the device to the guest.


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Press the green tick button to add the new device.

4. Creating the guest with virt-installAppend the following parameter exactly as listed below to add the driver disk to the installationwith the virt-install command :

--disk path=/usr/share/virtio-win/virtio-drivers.vfd,device=floppy

5. During the installation, additional steps are required to install drivers, depending on the type ofWindows guest.

a. Windows Server 2003 and Windows XPBefore the installation blue screen repeatedly press F6 for third party drivers.


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Press S to install additional

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Press Enter to continue the installation.

b. Windows Server 2008Install the guest as described by Section 9.1, “Using virt-install to create a guest”

When the installer prompts you for the driver, click on Load Driver, point the installer toDrive A: and pick the driver that suits your guest operating system and architecture.

11.3. Using KVM para-virtualized drivers for existingdevicesYou can modify an existing hard disk device attached to the guest to use the virtio driver instead ofthe virtualized IDE driver. This example edits libvirt configuration files. Alternatively, virt-manager,virsh attach-disk or virsh attach-interface can add a new device using the para-virtualized drivers Section 11.4, “Using KVM para-virtualized drivers for new devices”. Note that theguest does not need to be shut down to perform these steps, however the change will not be applieduntil the guest is completely shut down and rebooted.

1. Run the virsh edit <guestname> command to edit the XML configuration file for your device.For example, virsh edit guest1. The configuration files are located in /etc/libvirt/qemu.

2. Below is a file-based block device using the virtualized IDE driver. This is a typical entry for avirtualized guest not using the para-virtualized drivers.

<disk type='file' device='disk'> <source file='/var/lib/libvirt/images/disk1.img'/> <target dev='hda' bus='ide'/></disk>

3. Change the entry to use the para-virtualized device by modifying the bus= entry to virtio. Notethat if the disk was previously IDE it will have a target similar to hda, hdb, or hdc and so on. Whenchanging to bus=virtio the target needs to be changed to vda, vdb, or vdc accordingly.

<disk type='file' device='disk'>


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<source file='/var/lib/libvirt/images/disk1.img'/> <target dev='vda' bus='virtio'/></disk>

4. Remove the address tag inside the disk tags. This must be done for this procedure to work.Libvirt will regenerate the address tag appropriately the next time the guest is started.

Please refer to the libvirt wiki: http://wiki.libvirt.org/page/Virtio for more details on using Virtio.

11.4. Using KVM para-virtualized drivers for new devicesThis procedure covers creating new devices using the KVM para-virtualized drivers with virt-manager.

Alternatively, the virsh attach-disk or virsh attach-interface commands can be used toattach devices using the para-virtualized drivers.

Install the drivers first

Ensure the drivers have been installed on the Windows guest before proceeding to install newdevices. If the drivers are unavailable the device will not be recognized and will not work.

Procedure 11.3. Starting the new device wizard1. Open the virtualized guest by double clicking on the name of the guest in virt-manager.

2. Open the Information tab by pressing the i information button.

Figure 11.1. The information tab button

3. In the information tab, press the Add Hardware button.

4. In the Adding Virtual Hardware tab select Storage or Network for the type of device. The storageand network device wizards are covered in procedures Procedure 11.4, “Adding a storage deviceusing the para-virtualized storage driver” and Procedure 11.5, “Adding a network device using thepara-virtualized network driver”

Procedure 11.4. Adding a storage device using the para-virtualized storage driver1. Select hardware type

Select Storage as the Hardware type.

http://wiki.libvirt.org/page/Virtio

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2. Select the storage device and driverCreate a new disk image or select a storage pool volume.

Set the Device type to Virtio Disk to use the para-virtualized drivers.


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3. Finish the procedureConfirm the details for the new device are correct.


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Press Finish to complete the procedure.

Procedure 11.5. Adding a network device using the para-virtualized network driver1. Select hardware type

Select Network as the Hardware type.


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2. Select the network device and driverSelect the network device from the Host device list.

Create a custom MAC address or use the one provided.

Set the Device model to virtio to use the para-virtualized drivers.


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3. Finish the procedureConfirm the details for the new device are correct.


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Press Finish to complete the procedure.

Once all new devices are added, reboot the guest. Windows guests may may not recognise thedevices until the guest is rebooted.

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PCI passthroughThis chapter covers using PCI passthrough with KVM.

Certain hardware platforms allow virtualized guests to directly access various hardware devices andcomponents. This process in virtualization is known as passthrough. Passthrough is known as deviceassignment in some of the KVM documentation and the KVM code.

The KVM hypervisor supports attaching PCI devices on the host system to virtualized guests.PCI passthrough allows guests to have exclusive access to PCI devices for a range of tasks. PCIpassthrough allows PCI devices to appear and behave as if they were physically attached to the guestoperating system. PCI passthrough can improve the I/O performance of devices attached to virtualizedguests.

Almost all PCI and PCI Express devices that support passthrough, except for graphics cards, can bedirectly attached to virtualized guests with PCI passthrough.

PCI passthrough is only available on hardware platforms supporting either Intel VT-d or AMD IOMMU.These Intel VT-d or AMD IOMMU extensions must be enabled in BIOS for PCI passthrough tofunction.

Red Hat Enterprise Linux 6.0 and newer supports hot plugging PCI passthrough devices intovirtualized guests.

Out of the 32 available PCI devices for a guest 4 are not removable. This means there are only 28PCI slots available for additional devices per guest. Every para-virtualized network or block deviceuses one slot. Each guest can use up to 28 additional devices made up of any combination of para-virtualized network, para-virtualized disk devices, or other PCI devices using VT-d.

Procedure 12.1. Preparing an Intel system for PCI passthrough1. Enable the Intel VT-d extensions

The Intel VT-d extensions provides hardware support for directly assigning a physical devices toguest.

The VT-d extensions are required for PCI passthrough with Red Hat Enterprise Linux. Theextensions must be enabled in the BIOS. Some system manufacturers disable these extensionsby default.

These extensions are often called various terms in BIOS which differ from manufacturer tomanufacturer. Consult your system manufacturer's documentation.

2. Activate Intel VT-d in the kernelActivate Intel VT-d in the kernel by appending the intel_iommu=on parameter to the kernel lineof the kernel line in the /boot/grub/grub.conf file.

The example below is a modified grub.conf file with Intel VT-d activated.

default=0timeout=5splashimage=(hd0,0)/grub/splash.xpm.gzhiddenmenutitle Red Hat Enterprise Linux Server (2.6.32-36.x86-645) root (hd0,0) kernel /vmlinuz-2.6.32-36.x86-64 ro root=/dev/VolGroup00/LogVol00 rhgb quiet intel_iommu=on initrd /initrd-2.6.32-36.x86-64.img

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3. Ready to useReboot the system to enable the changes. Your system is now PCI passthrough capable.

Procedure 12.2. Preparing an AMD system for PCI passthrough• Enable AMD IOMMU extensions

The AMD IOMMU extensions are required for PCI passthrough with Red Hat Enterprise Linux.The extensions must be enabled in the BIOS. Some system manufacturers disable theseextensions by default.

AMD systems only require that the IOMMU is enabled in the BIOS. The system is ready for PCIpassthrough once the IOMMU is enabled.

12.1. Adding a PCI device with virshThese steps cover adding a PCI device to a virtualized guest on a KVM hypervisor using hardware-assisted PCI passthrough.

This example uses a USB controller device with the PCI identifier code, pci_8086_3a6c, and a fullyvirtualized guest named win2k3.

1. Identify the deviceIdentify the PCI device designated for passthrough to the guest. The virsh nodedev-listcommand lists all devices attached to the system. The --tree option is useful for identifyingdevices attached to the PCI device (for example, disk controllers and USB controllers).

# virsh nodedev-list --tree

For a list of only PCI devices, run the following command:

# virsh nodedev-list | grep pci

In the output from this command, each PCI device is identified by a string, as shown in thefollowing example output:

pci_0000_00_00_0pci_0000_00_02_0pci_0000_00_02_1pci_0000_00_03_0pci_0000_00_03_2pci_0000_00_03_3pci_0000_00_19_0pci_0000_00_1a_0pci_0000_00_1a_1pci_0000_00_1a_2pci_0000_00_1a_7pci_0000_00_1b_0pci_0000_00_1c_0

Tip: determining the PCI device

Comparing lspci output to lspci -n (which turns off name resolution) output can assist inderiving which device has which device identifier code.

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Record the PCI device number; the number is needed in other steps.

2. Information on the domain, bus and function are available from output of the virsh nodedev-dumpxml command:

# virsh nodedev-dumpxml pci_8086_3a6c<device> <name>pci_8086_3a6c</name> <parent>computer</parent> <capability type='pci'> <domain>0</domain> <bus>0</bus> <slot>26</slot> <function>7</function> <id='0x3a6c'>82801JD/DO (ICH10 Family) USB2 EHCI Controller #2</product> <vendor id='0x8086'>Intel Corporation</vendor> </capability></device>

3. Detach the device from the system. Attached devices cannot be used and may cause variouserrors if connected to a guest without detaching first.

# virsh nodedev-dettach pci_8086_3a6c Device pci_8086_3a6c dettached

4. Convert slot and function values to hexadecimal values (from decimal) to get the PCI busaddresses. Append "0x" to the beginning of the output to tell the computer that the value is ahexadecimal number.

For example, if bus = 0, slot = 26 and function = 7 run the following:

$ printf %x 00$ printf %x 261a$ printf %x 77

The values to use:

bus='0x00'slot='0x1a'function='0x7'

5. Run virsh edit (or virsh attach device) and added a device entry in the <devices> section toattach the PCI device to the guest.

# virsh edit win2k3<hostdev mode='subsystem' type='pci' managed='yes'> <source> <address domain='0x0000' bus='0x00' slot='0x1a' function='0x7'/> </source></hostdev>

6. Once the guest system is configured to use the PCI address, the host system must be configuredto stop using the device. The ehci driver is loaded by default for the USB PCI controller.


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$ readlink /sys/bus/pci/devices/0000\:00\:1a.7/driver../../../bus/pci/drivers/ehci_hcd

7. Detach the device:

$ virsh nodedev-dettach pci_8086_3a6c

8. Verify it is now under the control of pci_stub:

$ readlink /sys/bus/pci/devices/0000\:00\:1d.7/driver../../../bus/pci/drivers/pci-stub

9. Set a sebool to allow the management of the PCI device from the guest:

$ setsebool -P virt_manage_sysfs 1

10. Start the guest system :

# virsh start win2k3

The PCI device should now be successfully attached to the guest and accessible to the guestoperating system.

12.2. Adding a PCI device with virt-managerPCI devices can be added to guests using the graphical virt-manager tool. The following procedureadds a 2 port USB controller to a virtualized guest.

1. Identify the deviceIdentify the PCI device designated for passthrough to the guest. The virsh nodedev-listcommand lists all devices attached to the system. The --tree option is useful for identifyingdevices attached to the PCI device (for example, disk controllers and USB controllers).





pci_0000_00_00_0pci_0000_00_02_0pci_0000_00_02_1pci_0000_00_03_0pci_0000_00_03_2pci_0000_00_03_3pci_0000_00_19_0pci_0000_00_1a_0pci_0000_00_1a_1pci_0000_00_1a_2

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pci_0000_00_1a_7pci_0000_00_1b_0pci_0000_00_1c_0



Record the PCI device number; the number is needed in other steps.

2. Detach the PCI deviceDetach the device from the system.

# virsh nodedev-dettach pci_8086_3a6c Device pci_8086_3a6c dettached

3. Open the hardware settingsOpen the virtual machine and click the Add Hardware button to add a new device to the guest.


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4. Add the new deviceSelect Physical Host Device from the Hardware type list. Click Forward to continue.

5. Select a PCI deviceSelect an unused PCI device. Note that selecting PCI devices presently in use on the host causeserrors. In this example a PCI to USB interface device is used.

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6. Confirm the new deviceClick the Finish button to confirm the device setup and add the device to the guest.


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The setup is complete and the guest can now use the PCI device.

12.3. PCI passthrough with virt-installTo use PCI passthrough with the virt-install parameter, use the additional --host-device parameter.

1. Identify the PCI deviceIdentify the PCI device designated for passthrough to the guest. The virsh nodedev-listcommand lists all devices attached to the system. The --tree option is useful for identifyingdevices attached to the PCI device (for example, disk controllers and USB controllers).





pci_0000_00_00_0

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pci_0000_00_02_0pci_0000_00_02_1pci_0000_00_03_0pci_0000_00_03_2pci_0000_00_03_3pci_0000_00_19_0pci_0000_00_1a_0pci_0000_00_1a_1pci_0000_00_1a_2pci_0000_00_1a_7pci_0000_00_1b_0pci_0000_00_1c_0



2. Add the deviceUse the PCI identifier output from the virsh nodedev command as the value for the --host-device parameter.

# virt-install \ -n hostdev-test -r 1024 --vcpus 2 \ --os-variant fedora11 -v \ -l http://download.fedoraproject.org/pub/fedora/linux/development/x86_64/os \ -x 'console=ttyS0 vnc' --nonetworks --nographics \ --disk pool=default,size=8 \ --debug --host-device=pci_8086_10bd

3. Complete the installationComplete the guest installation. The PCI device should be attached to the guest.

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SR-IOV

13.1. IntroductionThe PCI-SIG (PCI Special Interest Group) developed the Single Root I/O Virtualization (SR-IOV)specification. The SR-IOV specification is a standard for a type of PCI passthrough which nativelyshares a single device to multiple guests. SR-IOV reduces hypervisor involvement by specifyingvirtualization compatible memory spaces, interrupts and DMA streams. SR-IOV improves deviceperformance for virtualized guests.

Figure 13.1. How SR-IOV works

SR-IOV enables a Single Root Function (for example, a single Ethernet port), to appear as multiple,separate, physical devices. A physical device with SR-IOV capabilities can be configured to appearin the PCI configuration space as multiple functions, each device has its own configuration spacecomplete with Base Address Registers (BARs).


• Physical Functions (PFs) are full PCIe devices that include the SR-IOV capabilities. PhysicalFunctions are discovered, managed, and configured as normal PCI devices. Physical Functionsconfigure and manage the SR-IOV functionality by assigning Virtual Functions.

• Virtual Functions (VFs) are simple PCIe functions that only process I/O. Each Virtual Function isderived from a Physical Function. The number of Virtual Functions a device may have is limitedby the device hardware. A single Ethernet port, the Physical Device, may map to many VirtualFunctions that can be shared to virtualized guests.

The hypervisor can map one or more Virtual Functions to a virtualized guest. The Virtual Function'sconfiguration space is mapped to the configuration space presented to the virtualized guest by thehypervisor.

Each Virtual Function can only be mapped to a single guest at a time, as Virtual Functions requirereal hardware resources. A virtualized guest can have multiple Virtual Functions. A Virtual Function

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appears as a network card in the same way as a normal network card would appear to an operatingsystem.

The SR-IOV drivers are implemented in the kernel. The core implementation is contained in the PCIsubsystem, but there must also be driver support for both the Physical Function (PF) and VirtualFunction (VF) devices. With an SR-IOV capable device one can allocate VFs from a PF. The VFsappear as PCI devices which are backed on the physical PCI device by resources (queues, andregister sets).

Migrating guests with SR-IOV is possible with the vhost-net feature.

Advantages of SR-IOVSR-IOV devices can share a single physical port with multiple virtualized guests.

Virtual Functions have near-native performance and provide better performance than para-virtualizeddrivers and emulated access. Virtual Functions provide data protection between virtualized guests onthe same physical server as the data is managed and controlled by the hardware.

These features allow for increased virtualized guest density on hosts within a data center.

SR-IOV is better able to utilize the bandwidth of devices with multiple guests.

13.2. Using SR-IOVThis section covers attaching Virtual Function to a guest as an additional network device.

SR-IOV requires Intel VT-d support.

Procedure 13.1. Attach an SR-IOV network device1. Enable Intel VT-d in BIOS and in the kernel

Skip this step if Intel VT-d is already enabled and working.

Enable Intel VT-D in BIOS if it is not enabled already. Refer to Procedure 12.1, “Preparing an Intelsystem for PCI passthrough” for procedural help on enabling Intel VT-d in BIOS and the kernel.

2. Verify supportVerify if the PCI device with SR-IOV capabilities are detected. This example lists an Intel 82576network interface card which supports SR-IOV. Use the lspci command to verify if the devicewas detected.

# lspci03:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)03:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)

Note that the output has been modified to remove all other devices.

3. Start the SR-IOV kernel modulesIf the device is supported the driver kernel module should be loaded automatically by the kernel.Optional parameters can be passed to the module using the modprobe command. The Intel82576 network interface card uses the igb driver kernel module.

# modprobe igb [<option>=<VAL1>,<VAL2>,]# lsmod |grep igbigb 87592 0dca 6708 1 igb

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4. Activate Virtual FunctionsThe max_vfs parameter of the igb module allocates the maximum number of Virtual Functions.The max_vfs parameter causes the driver to spawn, up to the value of the parameter in, VirtualFunctions. For this particular card the valid range is 0 to 7.

Remove the module to change the variable.

# modprobe -r igb

Restart the module with the max_vfs set to 1 or any number of Virtual Functions up to themaximum supported by your device.

# modprobe igb max_vfs=7

5. Make the Virtual Functions persistentThe modprobe command /etc/modprobe.d/igb.conf options igb max_vfs=7

6. Inspect the new Virtual FunctionsUsing the lspci command, list the newly added Virtual Functions attached to the Intel 82576network device.

# lspci | grep 825760b:00.0 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)0b:00.1 Ethernet controller: Intel Corporation 82576 Gigabit Network Connection (rev 01)0b:10.0 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:10.1 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:10.2 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:10.3 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:10.4 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:10.5 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:10.6 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:10.7 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:11.0 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:11.1 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:11.2 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:11.3 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:11.4 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)0b:11.5 Ethernet controller: Intel Corporation 82576 Virtual Function (rev 01)

The identifier for the PCI device is found with the -n parameter of the lspci command. ThePhysical Functions corresponds to 0b:00.0 and 0b:00.1. All the Virtual Functions haveVirtual Function in the description.

7. Verify devices exist with virshThe libvirt service must recognize the device before adding a device to a guest. libvirtuses a similar notation to the lspci output. All punctuation characters, ; and ., in lspci outputare changed to underscores (_).

Use the virsh nodedev-list command and the grep command to filter the Intel 82576network device from the list of available host devices. 0b is the filter for the Intel 82576 networkdevices in this example. This may vary for your system and may result in additional devices.

# virsh nodedev-list | grep 0bpci_0000_0b_00_0pci_0000_0b_00_1pci_0000_0b_10_0pci_0000_0b_10_1

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pci_0000_0b_10_2pci_0000_0b_10_3pci_0000_0b_10_4pci_0000_0b_10_5pci_0000_0b_10_6pci_0000_0b_11_7pci_0000_0b_11_1pci_0000_0b_11_2pci_0000_0b_11_3pci_0000_0b_11_4pci_0000_0b_11_5

The serial numbers for the Virtual Functions and Physical Functions should be in the list.

8. Get device details with virshThe pci_0000_0b_00_0 is one of the Physical Functions and pci_0000_0b_10_0 is the firstcorresponding Virtual Function for that Physical Function. Use the virsh nodedev-dumpxmlcommand to get advanced output for both devices.

<device> <name>pci_0000_0b_00_0</name> <parent>pci_0000_00_01_0</parent> <driver> <name>igb</name> </driver> <capability type='pci'> <domain>0</domain> <bus>11</bus> <slot>0</slot> <function>0</function> <product id='0x10c9'>Intel Corporation</product> <vendor id='0x8086'>82576 Gigabit Network Connection</vendor> </capability> </device># virsh nodedev-dumpxml pci_0000_0b_10_0 <device> <name>pci_0000_0b_10_0</name> <parent>pci_0000_00_01_0</parent> <driver> <name>igbvf</name> </driver> <capability type='pci'> <domain>0</domain> <bus>11</bus> <slot>16</slot> <function>0</function> <product id='0x10ca'>Intel Corporation</product> <vendor id='0x8086'>82576 Virtual Function</vendor> </capability> </device>

This example adds the Virtual Function pci_0000_0b_10_0 to the guest in Step 10. Note thebus, slot and function parameters of the Virtual Function, these are required for adding thedevice.

9. Detach the Virtual FunctionsDevices attached to a host cannot be attached to guests. Red Hat Enterprise Linux automaticallyattaches new devices to the host. Detach the Virtual Function from the host so that the VirtualFunction can be used by the guest. Detaching the Physical Function causes errors, only detachthe required Virtual Functions.

# virsh nodedev-dettach pci_0000_0b_10_0

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Device pci_0000_0b_10_0 dettached

10. Add the Virtual Function to the guesta. Shut down the guest.

b. Use the output from the virsh nodedev-dumpxml pci_8086_10ca_0 command tocalculate the values for the configuration file. Convert slot and function values to hexadecimalvalues (from decimal) to get the PCI bus addresses. Append "0x" to the beginning of theoutput to tell the computer that the value is a hexadecimal number.

The example device has the following values: bus = 3, slot = 16 and function = 1. Use theprintf utility to convert decimal values to hexadecimal values.

$ printf %x 33$ printf %x 1610$ printf %x 11

This example would use the following values in the configuration file:

bus='0x03'slot='0x10'function='0x01'

c. Open the XML configuration file with the virsh edit command. This example edits a guestnamed MyGuest.

# virsh edit MyGuest

d. The default text editor will open the libvirt configuration file for the guest. Add the new deviceto the devices section of the XML configuration file.

<hostdev mode='subsystem' type='pci'> <source> <address bus='0x03' slot='0x10' function='0x01'/> </source></hostdev>

e. Save the configuration.

11. RestartRestart the guest to complete the installation.

# virsh start MyGuest

The guest should start successfully and detect a new network interface card. This new card is theVirtual Function of the SR-IOV device.

13.3. Troubleshooting SR-IOVThis section contains some issues and solutions for problems which may affect SR-IOV.

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Error starting the guestStart the configured vm , an error reported as follows:

# virsh start testerror: Failed to start domain testerror: internal error unable to start guest: char device redirected to/dev/pts/2get_real_device: /sys/bus/pci/devices/0000:03:10.0/config: Permission deniedinit_assigned_device: Error: Couldn't get real device (03:10.0)!Failed to initialize assigned device host=03:10.0

This error is often caused by a device which is already assigned to another guest or to the host itself.

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KVM guest timing managementVirtualization poses various challenges for guest time keeping. Guests using the Time Stamp Counter(TSC) as a clock source may suffer timing issues as some CPUs do not have a constant Time StampCounter. Guests without accurate timekeeping may have issues with some networked applications andprocesses as the guest will run faster or slower than the actual time and fall out of synchronization.

KVM works around this issue by providing guests with a para-virtualized clock. Alternatively, someguests may use other x86 clock sources for their timing in future versions of those operating systems.

Guests can have several problems caused by inaccurate clocks and counters:

• Clocks can fall out of synchronization with the actual time which invalidates sessions and affectsnetworks.

• Guests with slower clocks may have issues migrating.

These problems exist on other virtualization platforms and timing should always be tested.

NTP

The Network Time Protocol (NTP) daemon should be running on the host and the guests. Enablethe ntpd service:

# service ntpd start

Add the ntpd service to the default startup sequence:

# chkconfig ntpd on

Using the ntpd service should minimize the affects of clock skew in all cases.

Determining if your CPU has the constant Time Stamp CounterYour CPU has a constant Time Stamp Counter if the constant_tsc flag is present. To determine ifyour CPU has the constant_tsc flag run the following command:

$ cat /proc/cpuinfo | grep constant_tsc

If any output is given your CPU has the constant_tsc bit. If no output is given follow the instructionsbelow.

Configuring hosts without a constant Time Stamp CounterSystems without constant time stamp counters require additional configuration. Power managementfeatures interfere with accurate time keeping and must be disabled for guests to accurately keep timewith KVM.

Note

These instructions are for AMD revision F cpus only.

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If the CPU lacks the constant_tsc bit, disable all power management features (BZ#5131381).Each system has several timers it uses to keep time. The TSC is not stable on the host, whichis sometimes caused by cpufreq changes, deep C state, or migration to a host with a fasterTSC. Deep C sleep states can stop the TSC. To prevent the kernel using deep C states appendprocessor.max_cstate=1 to the kernel boot options in the grub.conf file on the host:

title Red Hat Enterprise Linux (2.6.32-36.x86-64) root (hd0,0) kernel /vmlinuz-2.6.32-36.x86-64 ro root=/dev/VolGroup00/LogVol00 rhgb quiet processor.max_cstate=1

Disable cpufreq (only necessary on hosts without the constant_tsc) by editing the /etc/sysconfig/cpuspeed configuration file and change the MIN_SPEED and MAX_SPEED variablesto the highest frequency available. Valid limits can be found in the /sys/devices/system/cpu/cpu*/cpufreq/scaling_available_frequencies files.

Using the para-virtualized clock with Red Hat Enterprise Linux guestsFor certain Red Hat Enterprise Linux guests, additional kernel parameters are required. Theseparameters can be set by appending them to the end of the /kernel line in the /boot/grub/grub.conf fileof the guest.

The table below lists versions of Red Hat Enterprise Linux and the parameters required for guests onsystems without a constant Time Stamp Counter.

Red Hat Enterprise Linux Additional guest kernel parameters6.0 AMD64/Intel 64 with thepara-virtualized clock

Additional parameters are not required

6.0 AMD64/Intel 64 without thepara-virtualized clock

notsc lpj=n

5.5 AMD64/Intel 64 with thepara-virtualized clock


5.5 AMD64/Intel 64 without thepara-virtualized clock

divider=10 notsc lpj=n

5.5 x86 with the para-virtualizedclock


5.5 x86 without the para-virtualized clock

divider=10 clocksource=acpi_pm lpj=n

5.4 AMD64/Intel 64 divider=10 notsc

5.4 x86 divider=10 clocksource=acpi_pm

5.3 AMD64/Intel 64 divider=10 notsc

5.3 x86 divider=10 clocksource=acpi_pm

4.8 AMD64/Intel 64 notsc divider=10

4.8 x86 clock=pmtmr divider=10

3.9 AMD64/Intel 64 Additional parameters are not required

3.9 x86 Additional parameters are not required

1 https://bugzilla.redhat.com/show_bug.cgi?id=513138

https://bugzilla.redhat.com/show_bug.cgi?id=513138


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Using the Real-Time Clock with Windows Server 2003 and Windows XP guestsWindows uses the both the Real-Time Clock (RTC) and the Time Stamp Counter (TSC). For Windowsguests the Real-Time Clock can be used instead of the TSC for all time sources which resolves guesttiming issues.

To enable the Real-Time Clock for the PMTIMER clock source (the PMTIMER usually uses the TSC)add the following line to the Windows boot settings. Windows boot settings are stored in the boot.inifile. Add the following line to the boot.ini file:

/use pmtimer

For more information on Windows boot settings and the pmtimer option, refer to Available switchoptions for the Windows XP and the Windows Server 2003 Boot.ini files2.

Using the Real-Time Clock with Windows Vista, Windows Server 2008 and Windows 7guestsWindows uses the both the Real-Time Clock (RTC) and the Time Stamp Counter (TSC). For Windowsguests the Real-Time Clock can be used instead of the TSC for all time sources which resolves guesttiming issues.

The boot.ini file is no longer used from Windows Vista and newer. Windows Vista, WindowsServer 2008 and Windows 7 use the Boot Configuration Data Editor (bcdedit.exe) to modify theWindows boot parameters.

This procedure is only required if the guest is having time keeping issues. Time keeping issues maynot affect guests on all host systems.

1. Open the Windows guest.

2. Open the Accessories menu of the start menu. Right click on the Command Promptapplication, select Run as Administrator.

3. Confirm the security exception, if prompted.

4. Set the boot manager to use the platform clock. This should instruct Windows to use the PM timerfor the primary clock source. The system UUID ({default} in the example below) should bechanged if the system UUID is different than the default boot device.

C:\Windows\system32>bcdedit /set {default} USEPLATFORMCLOCK onThe operation completed successfully

This fix should improve time keeping for Windows Vista, Windows Server 2008 and Windows 7guests.

2 http://support.microsoft.com/kb/833721

http://support.microsoft.com/kb/833721



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Part IV. Administration

Administering virtualized systemsThese chapters contain information for administering host and virtualized guests using tools includedin Red Hat Enterprise Linux 6.

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Server best practicesThe following tasks and tips can assist you with securing and ensuring reliability of your Red HatEnterprise Linux host.

• Run SELinux in enforcing mode. Set SELinux to run in enforcing mode with the setenforcecommand.

# setenforce 1

• Remove or disable any unnecessary services such as AutoFS, NFS, FTP, HTTP, NIS, telnetd,sendmail and so on.

• Only add the minimum number of user accounts needed for platform management on the serverand remove unnecessary user accounts.

• Avoid running any unessential applications on your host. Running applications on the host mayimpact virtual machine performance and can affect server stability. Any application which may crashthe server will also cause all virtual machines on the server to go down.

• Use a central location for virtual machine installations and images. Virtual machine images shouldbe stored under /var/lib/libvirt/images/. If you are using a different directory for yourvirtual machine images make sure you add the directory to your SELinux policy and relabel it beforestarting the installation.

• Installation sources, trees, and images should be stored in a central location, usually the location ofyour vsftpd server.

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Security for virtualizationWhen deploying virtualization technologies on your corporate infrastructure, you must ensure thatthe host cannot be compromised. The host is a Red Hat Enterprise Linux system that manages thesystem, devices, memory and networks as well as all virtualized guests. If the host is insecure, allguests in the system are vulnerable. There are several ways to enhance security on systems usingvirtualization. You or your organization should create a Deployment Plan containing the operatingspecifications and specifies which services are needed on your virtualized guests and host servers aswell as what support is required for these services. Here are a few security issues to consider whiledeveloping a deployment plan:

• Run only necessary services on hosts. The fewer processes and services running on the host, thehigher the level of security and performance.

• Enable SELinux on the hypervisor. Read Section 16.2, “SELinux and virtualization” for moreinformation on using SELinux and virtualization.

• Use a firewall to restrict traffic to the host. You can setup a firewall with default-reject rules that willhelp secure the host from attacks. It is also important to limit network-facing services.

• Do not allow normal users to access the host. The host is privileged, and granting access tounprivileged accounts may compromise the level of security.

16.1. Storage security issuesAdministrators of virtualized guests can change the partitions the host boots in certain circumstances.To prevent this administrators should follow these recommendations:

The host should not use disk labels to identify file systems in the fstab file, the initrd file or usedby the kernel command line. If less privileged users, especially virtualized guests, have write access towhole partitions or LVM volumes.

Guests should not be given write access to whole disks or block devices (for example, /dev/sdb).Use partitions (for example, /dev/sdb1) or LVM volumes.

16.2. SELinux and virtualizationSecurity Enhanced Linux was developed by the NSA with assistance from the Linux community toprovide stronger security for Linux. SELinux limits an attackers abilities and works to prevent manycommon security exploits such as buffer overflow attacks and privilege escalation. It is because ofthese benefits that all Red Hat Enterprise Linux systems should run with SELinux enabled and inenforcing mode.

SELinux prevents guest images from loading if SELinux is enabled and the images are not in thecorrect directory. SELinux requires that all guest images are stored in /var/lib/libvirt/images.

Adding LVM based storage with SELinux in enforcing modeThe following section is an example of adding a logical volume to a virtualized guest with SELinuxenabled. These instructions also work for hard drive partitions.

Procedure 16.1. Creating and mounting a logical volume on a virtualized guest with SELinux enabled1. Create a logical volume. This example creates a 5 gigabyte logical volume named

NewVolumeName on the volume group named volumegroup.

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# lvcreate -n NewVolumeName -L 5G volumegroup

2. Format the NewVolumeName logical volume with a file system that supports extended attributes,such as ext3.

# mke2fs -j /dev/volumegroup/NewVolumeName

3. Create a new directory for mounting the new logical volume. This directory can be anywhere onyour file system. It is advised not to put it in important system directories (/etc, /var, /sys) or inhome directories (/home or /root). This example uses a directory called /virtstorage

# mkdir /virtstorage

4. Mount the logical volume.

# mount /dev/volumegroup/NewVolumeName /virtstorage

5. Set the correct SELinux type for the libvirt image folder.

# semanage fcontext -a -t virt_image_t "/virtstorage(/.*)?"

If the targeted policy is used (targeted is the default policy) the command appends a line to the /etc/selinux/targeted/contexts/files/file_contexts.local file which makes thechange persistent. The appended line may resemble this:

/virtstorage(/.*)? system_u:object_r:virt_image_t:s0

6. Run the command to change the type of the mount point (/virtstorage) and all files under it tovirt_image_t (the restorecon and setfiles commands read the files in /etc/selinux/targeted/contexts/files/).

# restorecon -R -v /virtstorage

Testing new attributes

Create a new file (using the touch command) on the file system.

# touch /virtstorage/newfile

Verify the file has been relabeled using the following command:

# sudo ls -Z /virtstorage-rw-------. root root system_u:object_r:virt_image_t:s0 newfile

The output shows that the new file has the correct attribute, virt_image_t.

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16.3. SELinuxThis sections contains topics to consider when using SELinux with your virtualization deployment.When you deploy system changes or add devices, you must update your SELinux policy accordingly.To configure an LVM volume for a guest, you must modify the SELinux context for the respectiveunderlying block device and volume group.

# semanage fcontext -a -t virt_image _t -f -b /dev/sda2# restorecon /dev/sda2

KVM and SELinuxThere are several SELinux Booleans which affect KVM and libvirt. These Booleans are listed below foryour convenience.

KVM SELinux BooleansSELinux Boolean Descriptionallow_unconfined_qemu_transitionDefault: off. This Boolean controls whether KVM guests can be

transitioned to unconfined users.

qemu_full_network Default: on. This Boolean controls full network access to KVMguests.

qemu_use_cifs Default: on. This Boolean controls KVM's access to CIFS orSamba file systems.

qemu_use_comm Default: off. This Boolean controls whether KVM can accessserial or parallel communications ports.

qemu_use_nfs Default: on. This Boolean controls KVM's access to NFS filesystems.

16.4. Virtualization firewall informationVarious ports are used for communication between virtualized guests and management utilities.

Guest network services

Any network service on a virtualized guest must have the applicable ports open on the guest toallow external access. If a network service on a guest is firewalled it will be inaccessible. Alwaysverify the guests network configuration first.

• ICMP requests must be accepted. ICMP packets are used for network testing. You cannot pingguests if ICMP packets are blocked.

• Port 22 should be open for SSH access and the initial installation.

• Ports 80 or 443 (depending on the security settings on the RHEV Manager) are used by the vdsm-reg service to communicate information about the host.

• Ports 5634 to 6166 are used for guest console access with the SPICE protocol.

• Ports 49152 to 49216 are used for migrations with KVM. Migration may use any port in this rangedepending on the number of concurrent migrations occurring.

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• Enabling IP forwarding (net.ipv4.ip_forward = 1) is also required for shared bridges andthe default bridge. Note that installing libvirt enables this variable so it will be enabled when thevirtualization packages are installed unless it was manually disabled.

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sVirtsVirt is a technology included in Red Hat Enterprise Linux 6 that integrates SELinux and virtualization.sVirt applies Mandatory Access Control (MAC) to improve security when using virtualized guests. Themain reasons for integrating these technologies are to improve security and harden the system againstbugs in the hypervisor that might be used as an attack vector aimed toward the host or to anothervirtualized guest.

This chapter describes how sVirt integrates with virtualization technologies in Red Hat EnterpriseLinux 6.

Non-virtualized environmentsIn a non-virtualized environment, hosts are separated from each other physically and each host hasa self-contained environment, consisting of services such as a web server, or a DNS server. Theseservices communicate directly to their own user space, host kernel and physical host, offering theirservices directly to the network. The following image represents a non-virtualized environment:

Virtualized environmentsIn a virtualized environment, several operating systems can run on a single host kernel and physicalhost. The following image represents a virtualized environment:

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17.1. Security and VirtualizationWhen services are not virtualized, machines are physically separated. Any exploit is usually containedto the affected machine, with the obvious exception of network attacks. When services are groupedtogether in a virtualized environment, extra vulnerabilities emerge in the system. If there is a securityflaw in the hypervisor that can be exploited by a guest instance, this guest may be able to not onlyattack the host, but also other guests running on that host. This is not theoretical; attacks already existon hypervisors. These attacks can extend beyond the guest instance and could expose other gueststo attack.

sVirt is an effort to isolate guests and limit their ability to launch further attacks if exploited. This isdemonstrated in the following image, where an attack can not break out of the virtualized guest andextend to another host instance:

SELinux introduces a pluggable security framework for virtualized instances in its implementationof Mandatory Access Control (MAC). The sVirt framework allows guests and their resources to beuniquely labeled. Once labeled, rules can be applied which can reject access between differentguests.

17.2. sVirt labelingLike other services under the protection of SELinux, sVirt uses process-based mechanisms andrestrictions to provide an extra layer of security over guest instances. Under typical use, you shouldnot even notice that sVirt is working in the background. This section describes the labeling features ofsVirt.

As shown in the following output, when using sVirt, each virtualized guest process is labeled and runswith a dynamically generated level. Each process is isolated from other VMs with different levels:

# ps -eZ | grep qemu

system_u:system_r:svirt_t:s0:c87,c520 27950 ? 00:00:17 qemu-kvmsystem_u:system_r:svirt_t:s0:c639,c757 27989 ? 00:00:06 qemu-system-x86

The actual disk images are automatically labeled to match the processes, as shown in the followingoutput:

# ls -lZ /var/lib/libvirt/images/*

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system_u:object_r:svirt_image_t:s0:c87,c520 image1

The following table outlines the different labels that can be assigned when using sVirt:

Table 17.1. sVirt labels

Type SELinux Context Description

Virtualized guest processes system_u:system_r:svirt_t:MCS1 MCS1 is a randomlyselected MCS field. Currentlyapproximately 500,000 labelsare supported.

Virtualized guest images system_u:object_r:svirt_image_t:MCS1Only svirt_t processes with thesame MCS fields are able toread/write these image filesand devices.

Virtualized guest shared read/write content

system_u:object_r:svirt_image_t:s0All svirt_t processes areallowed to write to thesvirt_image_t:s0 files anddevices.

Virtualized guest shared readonly content

system_u:object_r:svirt_content_t:s0All svirt_t processes are ableto read files/devices with thislabel.

Virtualized guest images system_u:object_r:virt_content_t:s0System default label usedwhen an image exits. No svirt_tvirtual processes are allowedto read files/devices with thislabel.

It is also possible to perform static labeling when using sVirt. Static labels allow the administrator toselect a specific label, including the MCS/MLS field, for a virtualized guest. Administrators who runstatically-labeled virtualized guests are responsible for setting the correct label on the image files.The virtualized guest will always be started with that label, and the sVirt system will never modify thelabel of a statically-labeled virtual machine's content. This allows the sVirt component to run in an MLSenvironment. You can also run multiple virtualized guests with different sensitivity levels on a system,depending on your requirements.

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KVM live migrationThis chapter covers migrating guests running on a KVM hypervisor to another KVM host.

Migration is the term for the process of moving a virtualized guest from one host to another. Migrationis a key feature of virtualization as software is completely separated from hardware. Migration is usefulfor:

• Load balancing - guests can be moved to hosts with lower usage when a host becomes overloaded.

• Hardware failover - when hardware devices on the host start to fail, guests can be safely relocatedso the host can be powered down and repaired.

• Energy saving - guests can be redistributed to other hosts and host systems powered off to saveenergy and cut costs in low usage periods.

• Geographic migration - guests can be moved to another location for lower latency or in seriouscircumstances.

Migrations can be performed live or offline. To migrate guests the storage must be shared. Migrationworks by sending the guests memory to the destination host. The shared storage stores the guest'sdefault file system. The file system image is not sent over the network from the source host to thedestination host.

An offline migration suspends the guest then moves an image of the guests memory to the destinationhost. The guest is resumed on the destination host and the memory the guest used on the source hostis freed.

The time an offline migration takes depends on network bandwidth and latency. If the network isexperiencing heavy use or low bandwidth the migration will take much longer.

A live migration keeps the guest running on the source host and begins moving the memory withoutstopping the guest. All modified memory pages are monitored for changes and sent to the destinationwhile the image is sent. The memory is updated with the changed pages. The process continues untilthe amount of pause time allowed for the guest equals the predicted time for the final few pages tobe transferred. KVM estimates the time remaining and attempts to transfer the maximum amountof page files from the source to the destination until KVM predicts the amount of remaining pagescan be transferred during a very brief time while the virtualized guest is paused. The registers areloaded on the new host and the guest is then resumed on the destination host. If the guest cannotbe merged (which happens when guests are under extreme loads) the guest is paused and then anoffline migration is started instead.

18.1. Live migration requirementsMigrating guests requires the following:

Migration requirements• A virtualized guest installed on shared networked storage using one of the following protocols:

• Fibre Channel

• iSCSI

• NFS

• GFS2

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• Two or more Red Hat Enterprise Linux systems of the same version with the same updates.

• Both systems must have the appropriate ports open.

• Both systems must have identical network configurations. All bridging and network configurationsmust be exactly the same on both hosts.

• Shared storage must mount at the same location on source and destination systems. The mounteddirectory name must be identical.

Configuring network storageConfigure shared storage and install a guest on the shared storage. For shared storage instructions,refer to Part V, “Virtualization storage topics”.

Alternatively, use the NFS example in Section 18.2, “Shared storage example: NFS for a simplemigration”.

18.2. Shared storage example: NFS for a simple migrationThis example uses NFS to share guest images with other KVM hosts. This example is not practical forlarge installations, this example is only for demonstrating migration techniques and small deployments.Do not use this example for migrating or running more than a few virtualized guests.

For advanced and more robust shared storage instructions, refer to Part V, “Virtualization storagetopics”

1. Export your libvirt image directoryAdd the default image directory to the /etc/exports file:

/var/lib/libvirt/images *.example.com(rw,no_root_squash,async)

Change the hosts parameter as required for your environment.

2. Start NFSa. Install the NFS packages if they are not yet installed:

# yum install nfs

b. Open the ports for NFS in iptables and add NFS to the /etc/hosts.allow file.

c. Start the NFS service:

# service nfs start

3. Mount the shared storage on the destinationOn the destination system, mount the /var/lib/libvirt/images directory:

# mount sourceURL:/var/lib/libvirt/images /var/lib/libvirt/images

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Locations must be the same on source and destination

Whichever directory is chosen for the guests must exactly the same on host and guest. Thisapplies to all types of shared storage. The directory must be the same or the migration willfail.

18.3. Live KVM migration with virshA guest can be migrated to another host with the virsh command. The migrate command acceptsparameters in the following format:

# virsh migrate --live GuestName DestinationURL

The GuestName parameter represents the name of the guest which you want to migrate.

The DestinationURL parameter is the URL or hostname of the destination system. The destinationsystem must run the same version of Red Hat Enterprise Linux, be using the same hypervisor andhave libvirt running.

Once the command is entered you will be prompted for the root password of the destination system.

Example: live migration with virshThis example migrates from test1.example.com to test2.example.com. Change the hostnames for your environment. This example migrates a virtual machine named RHEL4test.

This example assumes you have fully configured shared storage and meet all the prerequisites (listedhere: Migration requirements).

1. Verify the guest is runningFrom the source system, test1.example.com, verify RHEL4test is running:

[root@test1 ~]# virsh listId Name State---------------------------------- 10 RHEL4 running

2. Migrate the guestExecute the following command to live migrate the guest to the destination,test2.example.com. Append /system to the end of the destination URL to tell libvirt that youneed full access.

# virsh migrate --live RHEL4test qemu+ssh://test2.example.com/system

Once the command is entered you will be prompted for the root password of the destinationsystem.

3. WaitThe migration may take some time depending on load and the size of the guest. virsh onlyreports errors. The guest continues to run on the source host until fully migrated.


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4. Verify the guest has arrived at the destination hostFrom the destination system, test2.example.com, verify RHEL4test is running:

[root@test2 ~]# virsh listId Name State---------------------------------- 10 RHEL4 running

The live migration is now complete.

Other networking methods

libvirt supports a variety of networking methods including TLS/SSL, unix sockets, SSH, andunencrypted TCP. Refer to Chapter 19, Remote management of virtualized guests for moreinformation on using other methods.

18.4. Migrating with virt-managerThis section covers migrating KVM based guests with virt-manager.

1. Connect to the source and the target hostsConnect to the source and target hosts. On the File menu, click Add Connection, the AddConnection window appears.

Enter the following details:

• Hypervisor: Select QEMU.

• Connection: Select the connection type.

• Hostname: Enter the hostname.

Press the Connect button.

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Figure 18.1. Add Connection

virt-manager now displays the newly connected host in the list of available hosts.


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Figure 18.2. Connected Host

2. Add a storage pool to both hostsBoth hosts must be connected to the same storage pool. Create the storage pool on both hostsusing the same network storage device. Using a storage pool ensures both servers have identicalstorage configurations. This procedure uses a NFS server.

a. Open the storage tabOn the Edit menu, click Host Details, the Host Details window appears.

Click the Storage tab.


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Figure 18.3. Storage tab

b. Add a storage pool with the same NFS to the source and target hosts.Add a new storage pool. In the lower left corner of the window, click the + button. The Add aNew Storage Pool window appears.

Enter the following details:

• Name: Enter the name of the storage pool.

• Type: Select netfs: Network Exported Directory.


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Figure 18.4. Add a new Storage Pool


c. Specify storage pool detailsEnter the following details:

• Format: Select the storage type. This must be NFS or iSCSI for live migrations.

• Host Name: Enter the IP address or fully-qualified domain name of the storage server.


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Figure 18.5. Storage pool details

Press the Finish button to add the storage pool.

d. Verify the new storage pool was added sucessfullyThe new storage pool should be visible in the Storage tab.


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Figure 18.6. New storage pool in the storage tab

Complete these steps on both hosts before proceeding.

3. Optional: Add a volume to the storage poolAdd a volume to the storage pool or create a new virtualized guest on the storage pool. If yourstorage pool already has virtualized guests, you can skip this step.

a. Create a new volume in the shared storage pool, click New Volume.

Enter the details, then click Create Volume.


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Figure 18.7. Add a storage volume

b. Create a new virtualized guest on the new volumeCreate a new virtualized guest that uses the new volume. For information on creatingvirtualized guests, refer to Part II, “Installation”.


150

Figure 18.8. New virtualized guest

The Virtual Machine window appears.


151

Figure 18.9. Virtual Machine window

4. Migrate the virtualized guestFrom the main virt-manager screen, right-click on the virtual machine and select Migrate.... TheMigrate the virtual machine window appears.


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Figure 18.10. Migrate the virtual machine

Select the destination host from the list.

Select Migrate offline to disable live migration and do an offline migration.

Select advanced options if required. For a standard migration, no of these settings should bemodified.

Press Migrate to confirm and migrate the virtualized guest.


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5. A status bar tracks the progress of the migration. Once the migration is complete the virtualizedguest will appear in the list of virtualized guests on the destination.

Figure 18.11. Completed migration

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Remote management of virtualizedguestsThis section explains how to remotely manage your virtualized guests using ssh or TLS and SSL.

19.1. Remote management with SSHThe ssh package provides an encrypted network protocol which can securely send managementfunctions to remote virtualization servers. The method described uses the libvirt managementconnection securely tunneled over an SSH connection to manage the remote machines. All theauthentication is done using SSH public key cryptography and passwords or passphrases gatheredby your local SSH agent. In addition the VNC console for each guest virtual machine is tunneled overSSH.

SSH is usually configured by default so you probably already have SSH keys setup and no extrafirewall rules needed to access the management service or VNC console.

Be aware of the issues with using SSH for remotely managing your virtual machines, including:• you require root log in access to the remote machine for managing virtual machines,

• the initial connection setup process may be slow,

• there is no standard or trivial way to revoke a user's key on all hosts or guests, and

• ssh does not scale well with larger numbers of remote machines.

Configuring password less or password managed SSH access for virt-managerThe following instructions assume you are starting from scratch and do not already have SSH keys setup. If you have SSH keys set up and copied to the other systems you can skip this procedure.

The user is important for remote management

SSH keys are user dependent. Only the user who owns the key may access that key.

virt-manager must run as the user who owns the keys to connect to the remote host. Thatmeans, if the remote systems are managed by a non-root user virt-manager must be run inunprivileged mode. If the remote systems are managed by the local root user then the SSH keysmust be owned and created by root.

You cannot manage the local host as an unprivileged user with virt-manager.

1. Optional: Changing userChange user, if required. This example uses the local root user for remotely managing the otherhosts and the local host.

$ su -

2. Generating the SSH key pairGenerate a public key pair on the machine virt-manager is used. This example uses thedefault key location, in the ~/.ssh/ directory.

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$ ssh-keygen -t rsa

3. Copying the keys to the remote hostsRemote login without a password, or with a passphrase, requires an SSH key to be distributed tothe systems being managed. Use the ssh-copy-id command to copy the key to root user at thesystem address provided (in the example, [email protected]).

$ ssh-copy-id -i ~/.ssh/id_rsa.pub [email protected]@example.com's password:

Now try logging into the machine, with the ssh [email protected] command and check in the.ssh/authorized_keys file to make sure unexpected keys have not been added.

Repeat for other systems, as required.

4. Optional: Add the passphrase to the ssh-agentAdd the passphrase for the SSH key to the ssh-agent, if required. On the local host, use thefollowing command to add the passphrase (if there was one) to enable password-less login.

# ssh-add ~/.ssh/id_rsa.pub

The SSH key was added to the remote system.

The libvirt daemon (libvirtd)The libvirt daemon provide an interface for managing virtual machines. You must have thelibvirtd daemon installed and running on every remote host that needs managing.

$ ssh root@somehost# chkconfig libvirtd on# service libvirtd start

After libvirtd and SSH are configured you should be able to remotely access and manage yourvirtual machines. You should also be able to access your guests with VNC at this point.

Accessing remote hosts with virt-managerRemote hosts can be managed with the virt-manager GUI tool. SSH keys must belong to the userexecuting virt-manager for password-less login to work.

1. Start virt-manager.

2. Open the File->Add Connection menu.

3. Input values for the hypervisor type, the connection, Connection->Remote tunnel over SSH, andenter the desired hostname, then click connection.

19.2. Remote management over TLS and SSLYou can manage virtual machines using TLS and SSL. TLS and SSL provides greater scalability butis more complicated than ssh (refer to Section 19.1, “Remote management with SSH”). TLS and SSLis the same technology used by web browsers for secure connections. The libvirt managementconnection opens a TCP port for incoming connections, which is securely encrypted and authenticatedbased on x509 certificates.

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TLS/SSL access for virt-managerThe libvirt Wiki contains complete details on how to configure TLS/SSL access: http://wiki.libvirt.org/page/TLSSetup

To enable SSL and TLS for VNC, refer to the libvirt Wiki: http://wiki.libvirt.org/page/VNCTLSSetup. It isnecessary to place the Certificate Authority Certificate, Client Certificate, and Client Certificate PrivateKey, in the following locations:

• The Certificate Authority Certificate should be placed in /etc/pki/CA/cacert.pem.

• The Client Certificate, signed by the CA, should be placed in either of:

• /etc/pki/libvirt-vnc/clientcert.pem for system wide use, or

• $HOME/.pki/libvirt-vnc/clientcert.pem for an individual user.

• The Private Key for the Client Certificate should be placed in either of:

• /etc/pki/libvirt-vnc/private/clientkey.pem for system wide use, or

• $HOME/.pki/libvirt-vnc/private/clientkey.pem for an individual user.

19.3. Transport modesFor remote management, libvirt supports the following transport modes:

Transport Layer Security (TLS)Transport Layer Security TLS 1.0 (SSL 3.1) authenticated and encrypted TCP/IP socket, usuallylistening on a public port number. To use this you will need to generate client and server certificates.The standard port is 16514.

UNIX socketsUnix domain sockets are only accessible on the local machine. Sockets are not encrypted, anduse UNIX permissions or SELinux for authentication. The standard socket names are /var/run/libvirt/libvirt-sock and /var/run/libvirt/libvirt-sock-ro (for read-onlyconnections).

SSHTransported over a Secure Shell protocol (SSH) connection. Requires Netcat (the nc package)installed. The libvirt daemon (libvirtd) must be running on the remote machine. Port 22 must beopen for SSH access. You should use some sort of ssh key management (for example, the ssh-agent utility) or you will be prompted for a password.

extThe ext parameter is used for any external program which can make a connection to the remotemachine by means outside the scope of libvirt. This parameter is unsupported.

tcpUnencrypted TCP/IP socket. Not recommended for production use, this is normally disabled, but anadministrator can enable it for testing or use over a trusted network. The default port is 16509.

The default transport, if no other is specified, is tls.

http://wiki.libvirt.org/page/TLSSetup

http://wiki.libvirt.org/page/TLSSetup

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Remote URIsA Uniform Resource Identifier (URI) is used by virsh and libvirt to connect to a remote host.URIs can also be used with the --connect parameter for the virsh command to execute singlecommands or migrations on remote hosts.

libvirt URIs take the general form (content in square brackets, "[]", represents optional functions):

driver[+transport]://[username@][hostname][:port]/[path][?extraparameters]

The transport method or the hostname must be provided to target an external location.

Examples of remote management parameters• Connect to a remote KVM host named server7, using SSH transport and the SSH usernameccurran.

qemu+ssh://ccurran@server7/

• Connect to a remote KVM hypervisor on the host named server7 using TLS.

qemu://server7/

• Connect to a remote KVM hypervisor on host server7 using TLS. The no_verify=1 instructslibvirt not to verify the server's certificate.

qemu://server7/?no_verify=1

Testing examples• Connect to the local KVM hypervisor with a non-standard UNIX socket. The full path to the Unix

socket is supplied explicitly in this case.

qemu+unix:///system?socket=/opt/libvirt/run/libvirt/libvirt-sock

• Connect to the libvirt daemon with an unencrypted TCP/IP connection to the server with the IPaddress 10.1.1.10 on port 5000. This uses the test driver with default settings.

test+tcp://10.1.1.10:5000/default

Extra URI parametersExtra parameters can be appended to remote URIs. The table below Table 19.1, “Extra URIparameters” covers the recognized parameters. All other parameters are ignored. Note that parametervalues must be URI-escaped (that is, a question mark (?) is appended before the parameter andspecial characters are converted into the URI format).

Table 19.1. Extra URI parameters

Name Transport mode Description Example usage

name all modes The name passedto the remotevirConnectOpenfunction. The nameis normally formed byremoving transport,

name=qemu:///system

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Name Transport mode Description Example usagehostname, portnumber, username andextra parameters fromthe remote URI, but incertain very complexcases it may be betterto supply the nameexplicitly.

command ssh and ext The externalcommand. For exttransport this isrequired. For ssh thedefault is ssh. ThePATH is searched forthe command.

command=/opt/openssh/bin/ssh

socket unix and ssh The path to the UNIXdomain socket, whichoverrides the default.For ssh transport, thisis passed to the remotenetcat command (seenetcat).

socket=/opt/libvirt/run/libvirt/libvirt-sock

netcat ssh The netcat commandcan be used to connectto remote systems.The default netcatparameter uses thenc command. ForSSH transport, libvirtconstructs an SSHcommand using theform below:

command -p port [-lusername] hostname

netcat -U socket

The port, usernameand hostnameparameters can bespecified as part ofthe remote URI. Thecommand, netcat andsocket come fromother extra parameters.

netcat=/opt/netcat/bin/nc

no_verify tls If set to a non-zerovalue, this disablesclient checks of theserver's certificate.Note that to disable

no_verify=1


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Name Transport mode Description Example usageserver checks of theclient's certificate orIP address you mustchange the libvirtdconfiguration.

no_tty ssh If set to a non-zerovalue, this stops sshfrom asking for apassword if it cannotlog in to the remotemachine automatically(for using ssh-agentor similar). Use thiswhen you do nothave access to aterminal - for examplein graphical programswhich use libvirt.

no_tty=1

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Overcommitting with KVMThe KVM hypervisor supports overcommitting CPUs and overcommitting memory. Overcommitting isallocating more virtualized CPUs or memory than there are physical resources on the system. WithCPU overcommit, under-utilized virtualized servers or desktops can run on fewer servers which savespower and money.

Overcommitting memoryMost operating systems and applications do not use 100% of the available RAM all the time. Thisbehavior can be exploited with KVM. KVM can allocate more memory for virtualized guests than thehost has physically available.

With KVM, virtual machines are Linux processes. Guests on the KVM hypervisor do not havededicated blocks of physical RAM assigned to them, instead guests function as Linux processes. TheLinux kernel allocates each process memory when the process requests more memory. KVM guestsare allocated memory when requested by the guest operating system. The guest only requires slightlymore physical memory than the virtualized operating system reports as used. The Linux kernel swapsinfrequently used memory out of physical memory and into virtual memory. Swapping decreases theamount of memory required by virtualized guests.

When physical memory is completely used or a process is inactive for some time, Linux moves theprocess's memory to swap. Swap is usually a partition on a hard disk drive or solid state drive whichLinux uses to extend virtual memory. Swap is significantly slower than RAM due to the throughput andresponse times of hard drives and solid state drives.

As KVM virtual machines are Linux processes, underused or idle memory of virtualized guests ismoved by default to swap. The total memory used by guests can be overcommitted, which is to usemore than the physically available host memory. Overcommitting requires sufficient swap space for allguests and all host processes.

Without sufficient swap space for all processes in virtual memory the pdflush process, the cleanupprocess, starts. The pdflush process kills processes to free memory so the system does not crash.pdflush may destroy virtualized guests or other system processes which may cause file systemerrors and may leave virtualized guests unbootable.This can cause issues if virtualized guests usetheir total RAM.

Warning

If sufficient swap is not available guest operating systems will be forcibly shut down. This mayleave guests inoperable. Avoid this by never overcommitting more memory than there is swapavailable.

Overcommitting with KSM

If KSM is used ensure the swap size is sufficient for the overcommitted RAM. KSM reducesthe RAM usage of identical or similar guests. Overcommitting guests with KSM withoutsufficient swap may be possible but is not recommended. For more information on KSM andovercommitting, refer to Chapter 21, KSM.

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Configuring swap for overcommitting memoryThe swap partition is used for swapping underused memory to the hard drive to speed up memoryperformance. The default size of the swap partition is calculated from the physical RAM of the host.

Red Hat Knowledgebase1 has an article on safely and efficiently determining the size of the swappartition.

The swap partition must be large enough to provide virtual memory for all guests and the host system.

Important

The example below is provided as a guide for configuring swap only. The settings listed may notbe appropriate for your environment.

Example 20.1. Memory overcommit exampleExampleServer1 has 32GB of RAM. The system is being configured to run 56 guests with 1GB ofvirtualized memory. The host system rarely uses more than 4GB of memory for system processes,drivers and storage caching.

32GB minus 4GB for the host leaves 28GB of physical RAM for virtualized guests. Each guest uses1GB of RAM, a total of 56GB of virtual RAM is required for the guests.

The Red Hat Knowledgebase recommends 8GB of swap for a system with 32GB of RAM. To safelyovercommit memory there must be sufficient virtual memory for all guests and the host. The hosthas 28GB of RAM for guests (which need 56GB of RAM). Therefore, the system needs at least28GB of swap for the guests.

ExampleServer1 requires at least 36GB (8GB for the host and 28GB for the guests) of swap tosafely overcommit for all 56 guests.

It is possible to overcommit memory over ten times the amount of physical RAM in the system. Thisonly works with certain types of guest, for example, desktop virtualization with minimal intensive usageor running several identical guests with KSM. Configuring swap and memory overcommit is not aformula, each environment and setup is different. Your environment must be tested and customized toensure stability and performance.

For more information on KSM and overcommitting, refer to Chapter 21, KSM.

Overcommitting virtualized CPUsThe KVM hypervisor supports overcommitting virtualized CPUs. Virtualized CPUs can beovercommitted as far as load limits of virtualized guests allow. Use caution when overcommittingVCPUs as loads near 100% may cause dropped requests or unusable response times.

Virtualized CPUs are overcommitted best when each virtualized guest only has a single VCPU. TheLinux scheduler is very efficient with this type of load. KVM should safely support guests with loadsunder 100% at a ratio of five VCPUs. Overcommitting single VCPU virtualized guests is not an issue.

You cannot overcommit symmetric multiprocessing guests on more than the physical number ofprocessing cores. For example a guest with four VCPUs should not be run on a host with a dual

1 http://kbase.redhat.com/faq/docs/DOC-15252

http://kbase.redhat.com/faq/docs/DOC-15252

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core processor. Overcommitting symmetric multiprocessing guests in over the physical number ofprocessing cores will cause significant performance degradation.

Assigning guests VCPUs up to the number of physical cores is appropriate and works as expected.For example, running virtualized guests with four VCPUs on a quad core host. Guests with less than100% loads should function effectively in this setup.

Always test first

Do not overcommit memory or CPUs in a production environment without extensive testing.Applications which use 100% of memory or processing resources may become unstable inovercommitted environments. Test before deploying.

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KSMThe concept of shared memory is common in modern operating systems. For example, when aprogram is first started it shares all of its memory with the parent program. When either the child orparent program tries to modify this memory, the kernel allocates a new memory region, copies theoriginal contents and allows the program to modify this new region. This is known as copy on write.

KSM is a new Linux feature which uses this concept in reverse. KSM enables the kernel to examinetwo or more already running programs and compare their memory. If any memory regions or pagesare identical, KSM reduces multiple references to multiple identical memory pages to a singlereference to a single page. This page is then marked copy on write. If the contents of the page ismodified, a new page is created.

This is useful for virtualization with KVM. When a virtualized guest is started, it only inherits thememory from the parent qemu-kvm process. Once the guest is running the contents of the guestoperating system image can be shared when guests are running the same operating system orapplications. KSM only identifies and merges identical pages which does not interfere with the guestor impact the security of the host or the guests. KSM allows KVM to request that these identical guestmemory regions be shared.

KSM provides enhanced memory speed and utilization. With KSM, common process data is storedin cache or in main memory. This reduces cache misses for the KVM guests which can improveperformance for some applications and operating systems. Secondly, sharing memory reduces theoverall memory usage of guests which allows for higher densities and greater utilization of resources.

Red Hat Enterprise Linux uses two separate methods for controlling KSM:

• The ksm service starts and stops the KSM kernel thread.

• The ksmtuned service controls and tunes the ksm, dynamically managing same-page merging. Theksmtuned service starts ksm and stops the ksm service if memory sharing is not necessary. Theksmtuned service must be told with the retune parameter to run when new virtualized guests arecreated or destroyed.

Both of these services are controlled with the standard service management tools.

The KSM serviceThe ksm service is a standard Linux daemon that uses the KSM kernel features.

KSM is included in the qemu-common package, which is a dependency of KVM. KSM is enabledby default in Red Hat Enterprise Linux. When the ksm service is not started, KSM shares only 2000pages. This default is low and provides limited memory saving benefits.

When the ksm service is started, KSM will share up to half of the host system's main memory. Start theksm service to enable KSM to share more memory.

# service ksm startStarting ksm: [ OK ]

The ksm service can be added to the default startup sequence. Make the ksm service persistent withthe chkconfig command.

# chkconfig ksm on

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The KSM tuning serviceThe ksmtuned service does not have any options. The ksmtuned service loops and adjusts ksm.The ksmtuned service is notified by libvirt when a virtualized guest is created or destroyed.

# service ksmtuned startStarting ksmtuned: [ OK ]

The ksmtuned service can be tuned with the retune parameter. The retune parameter instructsksmtuned to run tuning functions manually.

The /etc/ksmtuned.conf file is the configuration file for the ksmtuned service. The file outputbelow is the default ksmtuned.conf file.

# Configuration file for ksmtuned.

# How long ksmtuned should sleep between tuning adjustments# KSM_MONITOR_INTERVAL=60

# Millisecond sleep between ksm scans for 16Gb server.# Smaller servers sleep more, bigger sleep less.# KSM_SLEEP_MSEC=10

# KSM_NPAGES_BOOST=300# KSM_NPAGES_DECAY=-50# KSM_NPAGES_MIN=64# KSM_NPAGES_MAX=1250

# KSM_THRES_COEF=20# KSM_THRES_CONST=2048

# uncomment the following to enable ksmtuned debug information# LOGFILE=/var/log/ksmtuned# DEBUG=1

KSM variables and monitoringKSM stores monitoring data in the /sys/kernel/mm/ksm/ directory. Files in this directory areupdated by the kernel and are an accurate record of KSM usage and statistics.

The variables in the list below are also configurable variables in the /etc/ksmtuned.conf file asnoted below.

The /sys/kernel/mm/ksm/ filesfull_scans

Full scans run.

pages_sharedTotal pages shared.

pages_sharingPages presently shared.

pages_to_scanPages not scanned.

pages_unsharedPages no longer shared.

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pages_volatileNumber of volatile pages.

runWhether the KSM process is running.

sleep_millisecsSleep milliseconds.

KSM tuning activity is stored in the /var/log/ksmtuned log file if the DEBUG=1 line is added tothe /etc/ksmtuned.conf file. The log file location can be changed with the LOGFILE parameter.Changing the log file location is not advised and may require special configuration of SELinux settings.

The /etc/sysconfig/ksm file can manually set a number or all pages used by KSM as notswappable.

1. Open the /etc/sysconfig/ksm file with a text editor.

# The maximum number of unswappable kernel pages# which may be allocated by ksm (0 for unlimited)# If unset, defaults to half of total memory# KSM_MAX_KERNEL_PAGES=

2. Uncomment the KSM_MAX_KERNEL_PAGES line to manually configure the number ofunswappable pages for KSM. Setting this variable to 0 configures KSM to keep all identical pagesin main memory which can improve performance if the system has sufficient main memory.

# The maximum number of unswappable kernel pages# which may be allocated by ksm (0 for unlimited)# If unset, defaults to half of total memoryKSM_MAX_KERNEL_PAGES=0

Deactivating KSMKSM has a performance overhead which may be too large for certain environments or host systems.

KSM can be deactivated by stopping the ksm service and the ksmtuned service. Stopping theservices deactivates KSM but does not persist after restarting.

# service ksm stopStopping ksm: [ OK ]# service ksmtuned stopStopping ksmtuned: [ OK ]

Persistently deactivate KSM with the chkconfig command. To turn off the services, run the followingcommands:

# chkconfig ksm off# chkconfig ksmtuned off

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Advanced virtualization administrationThis chapter covers advanced administration tools for fine tuning and controlling virtualized guests andhost system resources.

Note

This chapter is a work in progress. Refer back to this document at a later date.

22.1. Guest schedulingKVM guests function as Linux processes. By default, KVM guests are prioritized and scheduled withthe Linux Completely Fair Scheduler. Tuning the schedule for guest processes may be required forsome environments or to prioritize certain guests.

22.2. Advanced memory managementCapping memory available to guests and preventing overcommit on certain guests.

22.3. Guest block I/O throttlingLimit guest block I/O throughput.

22.4. Guest network I/O throttlingLimit guest network activity.

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Migrating to KVM from otherhypervisors using virt-v2vThe virt-v2v command converts guests from a foreign hypervisor to run on KVM, managed bylibvirt. The virt-v2v command can currently convert Red Hat Enterprise Linux 4, Red Hat EnterpriseLinux 5, Windows Vista, Windows 7, Windows Server 2003 and Windows Server 2008 virtualizedguests running on Xen, KVM and VMware ESX. The virt-v2v command enables para-virtualized(virtio) drivers in the converted guest if possible.

virt-v2v is available on Red Hat Network (RHN) in the Red Hat Enterprise Linux Server (v. 6 for64-bit x86_64) or Red Hat Enterprise Linux Workstation (v.6 for x86_64) channel.

The virt-v2v tool requires root access to the host system.

Installing virt-v2vTo install virt-v2v from RHN, ensure the system is subscribed to the appropriate channel, then run:

yum install virt-v2v

23.1. Preparing to convert a virtualized guestBefore a virtualized guest can be converted, ensure that the following steps are completed.

1. Create a local storage domain for transferred storage

virt-v2v copies the guest storage to a locally defined libvirt storage pool during import. Thispool can be defined using any libvirt tool, and can be of any type. The simplest way to create anew pool is with virt-manager. Select your host, right click and select details.

Figure 23.1. Select host details

Select the Storage tab.

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Figure 23.2. The storage tab

Click the plus sign (+) button to add a new storage pool.

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Figure 23.3. Adding a storage pool

2. Create local network interfaces.

The local machine must have an appropriate network to which the converted virtualized guest canconnect. This is likely to be a bridge interface. A bridge interface can be created using standardtools on the host. Since version 0.8.3, virt-manager can also create and manage bridges.

3. Specify network mappings in virt-v2v.conf. This step is optional, and is not required for mostuse cases.

If your virtualized guest has multiple network interfaces, /etc/virt-v2v.conf must be editedto specify the network mapping for all interfaces. You can specify an alternative virt-v2v.conffile with the -f parameter.

If your virtualized guest only has a single network interface, it is simpler to use the --network or--bridge parameters, rather than modifying virt-v2v.conf.

Preparing to convert a virtualized guest running LinuxBefore a virtualized guest running Linux can be converted, ensure that the following steps arecompleted.

1. Obtain the software

As part of the conversion process, virt-v2v may install a new kernel and drivers on thevirtualized guest. If the host running virt-v2v is registered to Red Hat Network (RHN), therequired packages will be automatically downloaded. For environments where RHN is notavailable, the virt-v2v.conf file references a list of RPMs used for this purpose. The RPMsrelevant to your virtualized guest must be downloaded manually from RHN and made availablein the directory specified by the path-root configuration element, which by default is /var/lib/


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virt-v2v/software/. virt-v2v will display an error similar to Example 23.1, “MissingPackage error” if software it depends upon for a particular conversion is not available.

Example 23.1. Missing Package error

virt-v2v: Installation failed because the following files referenced in the configuration file are required, but missing:rhel/5/kernel-2.6.18-128.el5.x86_64.rpmrhel/5/ecryptfs-utils-56-8.el5.x86_64.rpmrhel/5/ecryptfs-utils-56-8.el5.i386.rpm

To obtain the relevant RPMs for your environment, repeat these steps for each missing package:

1. Login to Red Hat Network

2. Select Channels

3. Use the Filter by Product Channel function to select the channel for the version of RedHat Enterprise Linux running on the virtualized guest. In the case of the example shown inExample 23.1, “Missing Package error”, the channel is Red Hat Enterprise Linux Server 5.3.

4. Select the Packages tab

5. Use the Filter by Package function to locate the missing package

6. Select the package exactly matching the one shown in the error message. For thethe example shown in Example 23.1, “Missing Package error”, the first package iskernel-2.6.18-128.el5.x86_64

7. Select Download Package at the bottom of the package details page

8. Save the downloaded package to the appropriate directory in /var/lib/virt-v2v/software. For Red Hat Enterprise Linux 5, the directory is /var/lib/virt-v2v/software/rhel/5

Preparing to convert a virtualized guest running WindowsBefore a virtualized guest running Windows can be converted, ensure that the following steps arecompleted.

Important

Virtualized guests running Windows can only be converted for output to Red Hat EnterpriseVirtualization. The conversion procedure depends on post-processing by the Red Hat EnterpriseVirtualization Manager for completion. See Section 23.4.2, “Configuration changes for Windowsvirtualized guests” for details of the process. Virtualized guests running Windows cannot beconverted for output to libvirt.

1. Obtain the Guest Tools ISO

As part of the conversion process for virtualized guests running Windows, the Red Hat EnterpriseVirtualization Manager will install drivers using the Guest Tools ISO. See Section 23.4.2,“Configuration changes for Windows virtualized guests” for details of the process. The Guest ToolsISO is obtained as follows:

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1. From the Red Hat Enterprise Virtualization Manager, Login to Red Hat Network

2. Click on Download Software

3. Select the Red Hat Enterprise Virtualization (x86-64) channel

4. Select the Red Hat Enterprise Virt Manager for Desktops (v.2 x86) or Red Hat EnterpriseVirt Manager for Desktops (v.2 x86) channel, as appropriate for your subscription.

5. Download Guest Tools ISO for 2.2 and save it locally

2. Upload the Guest Tools ISO to the Red Hat Enterprise Virtualization Manager

Upload the Guest Tools ISO using the ISO Uploader. See the Red Hat Enterprise Virtualization forServers Administration Guide for instructions.

3. Ensure that the libguestfs-winsupport package is installed on the host running virt-v2v. Thispackage provides support for NTFS, which is used by many Windows systems. If you attempt toconvert a virtualized guest using NTFS without the libguestfs-winsupport package installed, theconversion will fail.

4. Ensure that the virtio-win package is installed on the host running virt-v2v. This packageprovides para-virtualized block and network drivers for Windows guests. If you attempt to converta virtualized guest running Windows without the virtio-win package installed, the conversion willfail giving an error message concerning missing files.

Preparing to convert a local Xen virtualized guestThe following is required when converting virtualized guests on a host which used to run Xen, but hasbeen updated to run KVM. It is not required when converting a Xen guest imported directly from arunning libvirt/Xen instance.

1. Obtain the XML for the virtualized guest

virt-v2v uses a libvirt domain description to determine the current configuration of thevirtualized guest, including the location of its storage. Before starting the conversion, obtain thisfrom the host running the virtualized guest with the following command:

virsh dumpxml vm-name > vm-name.xml

This will require booting into a Xen kernel to obtain the XML, as libvirt needs to connect to arunning Xen hypervisor to obtain its metadata. The conversion process is optimized for KVM, soobtaining domain data while running a Xen kernel, then performing the conversion using a KVMkernel will be more efficient than running the conversion on a Xen kernel.

23.2. Converting virtualized guestsOnce you have prepared to convert the virtualized guests, use virt-v2v to perform the actualconversions. This section provides the steps to convert the virtualized guests, and the reference tablefor virt-v2v. Note that conversions are resource intensive processes, involving copying the wholedisk image for a virtualized guest. In typical environments, converting a single virtualized guest takesapproximately 5-10 minutes.

23.2.1. virt-v2vvirt-v2v converts guests from a foreign hypervisor to run on KVM, managed by libvirt.


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virt-v2v -i libvirtxml -op pool --bridge brname vm-name.xmlvirt-v2v -op pool --network netname vm-namevirt-v2v -ic esx://esx.example.com/?no_verify=1 -op pool --bridge brname vm-name

Parameters

-i input Specifies the input method to obtain the guest for conversion. Thedefault is libvirt. Supported options are:• libvirt Guest argument is the name of a libvirt domain.

• libvirtxml Guest argument is the path to an XML file containinga libvirt domain.

-ic URI Specifies the connection to use when using the libvirt input method. Ifomitted, this defaults to qemu:///system.

virt-v2v can currently automatically obtain guest storage from locallibvirt connections, ESX connections, and connections over SSH.Other types of connection are not supported.

-o method Specifies the output method. If no output method is specified, thedefault is libvirt. Supported output methods are:

• libvirt, create a libvirt guest. See the -oc and -op options. -opmust be specified for the libvirt output method.

• rhev, create a guest on a Red Hat Enterprise Virtualization Exportstorage domain, which can later be imported using the manager.The -osd or Export storage domain must be specified for the rhevoutput method.

-oc URI Specifies the libvirt connection to use to create the converted guest.If omitted, this defaults to qemu:///system. Note that virt-v2v must beable to write directly to storage described by this libvirt connection.This makes writing to a remote connection impractical at present.

-op pool Specifies the pool which will be used to create new storage for theconverted guest.

-osd domain Specifies the path to an existing Red Hat Enterprise VirtualizationExport storage domain.

The domain must be in the format <host > <path>; for example, storage.example.com:/rhev/export. The nfs export must bemountable and writable by the machine running virt-v2v.

-f file | --configfile

Load the virt-v2v configuration from file. Defaults to /etc/virt-v2v.conf ifit exists.

-n network | --network network

Map all guest bridges or networks which don't have a mapping in theconfiguration file to the specified network.

This option cannot be used in conjunction with --bridge.

-b bridge | --bridgebridge

Map all guest bridges or networks which don't have a mapping in theconfiguration file to the specified bridge.

This option cannot be used in conjunction with --network.

--help Display brief help.

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--version Display version number and exit.

23.2.2. Converting a local Xen virtualized guestEnsure that the virtualized guest's XML is available locally, and that the storage referred to in the XMLis available locally at the same paths.

To convert the virtualized guest from an XML file, run:

virt-v2v -i libvirtxml -op pool --bridge brname vm-name.xml

Where pool is the local storage pool to hold the image, brname is the name of a local network bridgeto connect the converted guest's network to, and vm-name.xml is the path to the virtualized guest'sexported XML. You may also use the --network parameter to connect to a locally managed network,or specify multiple mappings in /etc/virt-v2v.conf.

If your guest uses a Xen para-virtualized kernel (it would be called something like kernel-xen orkernel-xenU), virt-v2v will attempt to install a new kernel during the conversion process. You canavoid this requirement by installing a regular kernel, which won't reference a hypervisor in its name,alongside the Xen kernel prior to conversion. You should not make this newly installed kernel yourdefault kernel, because Xen will not boot it. virt-v2v will make it the default during conversion.

23.2.3. Converting a remote Xen virtualized guestXen virtualized guests can be converted remotely via SSH. Ensure that the host running the virtualizedguest is accessible via SSH.

To convert the virtualized guest, run:

virt-v2v -ic xen+ssh://[email protected] -op pool --bridge brname vm-name

Where vmhost.example.com is the host running the virtualized guest, pool is the local storagepool to hold the image, brname is the name of a local network bridge to connect the convertedguest's network to, and vm-name is the domain of the Xen virtualized guest. You may also use the --network parameter to connect to a locally managed network, or specify multiple mappings in /etc/virt-v2v.conf.


23.2.4. Converting a VMware ESX virtualized guestEnsure that the virtualized guest is stopped prior to running the v2v process.

To convert the virtualized guest, run:

virt-v2v -ic esx://esx.example.com/ -op pool --bridge brname vm-name

Where esx.example.com is the VMware ESX server, pool is the local storage pool to hold theimage, brname is the name of a local network bridge to connect the converted guest's network to,and vm-name is the name of the virtualized guest. You may also use the --network parameter toconnect to a locally managed network, or specify multiple mappings in /etc/virt-v2v.conf.


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Authenticating to the ESX serverConnecting to the ESX server will require authentication. virt-v2v supports password authenticationwhen connecting to ESX. It reads passwords from $HOME/.netrc. The format of this file is described inthe netrc(5) man page. An example entry is:

machine esx.example.com login root password s3cr3t

.netrc permissions

The .netrc file must have a permission mask of 0600 to be read correctly by virt-v2v

Connecting to an ESX server with an invalid certificateIn non-production environments, the ESX server may have a non-valid certificate, for example a self-signed certificate. In this case, certificate checking can be explicitly disabled by adding '?no_verify=1'to the connection URI as shown below:

... -ic esx://esx.example.com/?no_verify=1 ...

23.2.5. Converting a virtualized guest running Windows

Important

Virtualized guests running Windows can only be converted for output to Red Hat EnterpriseVirtualization. The conversion procedure depends on post-processing by the Red Hat EnterpriseVirtualization Manager for completion. See Section 23.4.2, “Configuration changes for Windowsvirtualized guests” for details of the process. Virtualized guests running Windows cannot beconverted for output to libvirt.

This example demonstrates converting a local Xen virtualized guest running Windows for output toRed Hat Enterprise Virtualization. Ensure that the virtualized guest's XML is available locally, and thatthe storage referred to in the XML is available locally at the same paths.

To convert the virtualized guest from an XML file, run:

virt-v2v -i libvirtxml -o rhev -osd storage.example.com:/exportdomain --network rhevm vm-name.xml

Where vm-name.xml is the path to the virtualized guest's exported xml, andstorage.example.com:/exportdomain is the export storage domain. You may also use the --network parameter to connect to a locally managed network, or specify multiple mappings in /etc/virt-v2v.conf.


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23.3. Running converted virtualized guestsOn successful completion, virt-v2v will create a new libvirt domain for the converted virtualizedguest with the same name as the original virtualized guest. It can be started as usual using libvirt tools,for example virt-manager.

Guest network configurationvirt-v2v cannot currently reconfigure a guest's network configuration. If the converted guest is notconnected to the same subnet as the source, its network configuration may have to be updated.

23.4. Configuration changesAs well as configuring libvirt appropriately, virt-v2v will make certain changes to a guest to enableit to run on a KVM hypervisor either with or without virtio drivers. These changes are specific tothe guest operating system. The details specified here pertain to supported Red Hat based Linuxdistributions and Windows.

23.4.1. Configuration changes for Linux virtualized guests

Table 23.1. virt-v2v changes to Linux virtualized guests

Change Description

Kernel Un-bootable, that is, xen para-virtualized, kernelswill be uninstalled. No new kernel will be installedif there is a remaining kernel which supportsvirtio. If no remaining kernel supports virtio andthe configuration file specifies a new kernel it willbe installed and configured as the default.

X reconfiguration If the guest has X configured, its display driverwill be updated. See GUEST DRIVERS for whichdriver will be used.

Rename block devices If changes have caused block devices to changename, these changes will be reflected in /etc/fstab

Configure device drivers Whether virtio or non-virtio drivers areconfigured, virt-v2v will ensure that the correctnetwork and block drivers are specified in themodprobe configuration.

initrd virt-v2v will ensure that the initrd for the defaultkernel supports booting the root device, whetherit is using virtio or not.

SELinux virt-v2v will initiate a relabel of the guest on thenext boot. This ensures that any changes it hasmade are correctly labeled according to theguest's local policy.

virt-v2v will configure the following drivers in a Linux guest:

Table 23.2. Configured drivers in a Linux Guest

Para-virtualized driver type Driver module

Display cirrus


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Para-virtualized driver type Driver module

Storage virtio_blk

Network virtio_net

In addition, initrd will preload the virtio_pci driver

Other drivers

Display cirrus

Block Virtualized IDE

Network Virtualized e1000

23.4.2. Configuration changes for Windows virtualized guests

Warning

Before converting Windows virtualized guests, ensure that the libguestfs-winsupport and virtio-win packages are installed on the host running virt-v2v. These packages provide supportfor NTFS and Windows para-virtualized block and network drivers. If you attempt to convert avirtualized guest using NTFS without the libguestfs-winsupport package installed, the conversionwill fail. If you attempt to convert a virtualized guest running Windows without the virtio-winpackage installed, the conversion will fail giving an error message concerning missing files.

virt-v2v can convert virtualized guests running Windows Vista, Windows 7, Windows Server 2003and Windows Server 2008. The conversion process for virtualized guests running Windows is slightlyto different to the process for virtualized guests running Linux. Windows virtualized guest images areconverted as follows:

1. virt-v2v installs virtio block drivers.

2. virt-v2v installs the CDUpgrader utility.

3. virt-v2v makes registry changes to include the virtio block drivers in the CriticalDeviceDatabasesection of the registry, and ensure the CDUpgrader service is started at the next boot.

At this point, virt-v2v has completed the conversion. The converted virtualized guest is nowbootable, but does not yet have all the drivers installed necessary to function correctly. The conversionmust be finished by the Red Hat Enterprise Virtualization Manager. The Manager performs thefollowing steps:

1. The virtualized guest is imported and run on the Manager. See the Red Hat EnterpriseVirtualization for Servers Administration Guide for details.

Important

The first boot stage can take several minutes to run, and must not be interrupted. It will runautomatically without any administrator intervention other than starting the virtualized guest.To ensure the process is not interrupted, no user should login to the virtualized guest until ithas quiesced. You can check for this in the Manager GUI.

2. The Manager attaches the Guest Tools CD to the virtual machine.

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Note

The Guest Tools ISO must be uploaded using the ISO Uploader for this step to succeed. SeePreparing to convert a virtualized guest running Windows for instructions.

3. CDUpgrader detects the Guest Tools CD and installs all the virtio drivers from it, including a re-install of the virtio block drivers.

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Chapter 24.

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Miscellaneous administration tasksThis chapter contain useful hints and tips to improve virtualization performance, scale and stability.

24.1. Automatically starting guestsThis section covers how to make virtualized guests start automatically during the host system's bootphase.

This example uses virsh to set a guest, TestServer, to automatically start when the host boots.

# virsh autostart TestServerDomain TestServer marked as autostarted

The guest now automatically starts with the host.

To stop a guest automatically booting use the --disable parameter

# virsh autostart --disable TestServerDomain TestServer unmarked as autostarted

The guest no longer automatically starts with the host.

24.2. Using qemu-imgThe qemu-img command line tool is used for formatting various file systems used by KVM. qemu-img should be used for formatting virtualized guest images, additional storage devices and networkstorage. qemu-img options and usages are listed below.

Formatting and creating new images or devicesCreate the new disk image filename of size size and format format.

# qemu-img create [-6] [-e] [-b base_image] [-f format] filename [size]

If base_image is specified, then the image will record only the differences from base_image. No sizeneeds to be specified in this case. base_image will never be modified unless you use the "commit"monitor command.

Convert an existing image to another formatThe convert option is used for converting a recognized format to another image format.

Command format:

# qemu-img convert [-c] [-e] [-f format] filename [-O output_format] output_filename

Convert the disk image filename to disk image output_filename using format output_format.The disk image can be optionally encrypted with the -e option or compressed with the -c option.

Only the qcow2 format supports encryption or compression. the compression is read-only. It meansthat if a compressed sector is rewritten, then it is rewritten as uncompressed data.

The encryption uses the AES format with very secure 128-bit keys. Use a long password (over 16characters) to get maximum protection.

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Image conversion is also useful to get smaller image when using a format which can grow, such asqcow or cow. The empty sectors are detected and suppressed from the destination image.

getting image informationthe info parameter displays information about a disk image. the format for the info option is asfollows:

# qemu-img info [-f format] filename

give information about the disk image filename. use it in particular to know the size reserved on diskwhich can be different from the displayed size. if vm snapshots are stored in the disk image, they aredisplayed too.

Supported formatsThe format of an image is usually guessed automatically. The following formats are supported:

rawRaw disk image format (default). This format has the advantage of being simple and easilyexportable to all other emulators. If your file system supports holes (for example in ext2 or ext3on Linux or NTFS on Windows), then only the written sectors will reserve space. Use qemu-imginfo to know the real size used by the image or ls -ls on Unix/Linux.

qcow2QEMU image format, the most versatile format. Use it to have smaller images (useful if your filesystem does not supports holes, for example: on Windows), optional AES encryption, zlib basedcompression and support of multiple VM snapshots.

qcowOld QEMU image format. Only included for compatibility with older versions.

cowUser Mode Linux Copy On Write image format. The cow format is included only for compatibilitywith previous versions. It does not work with Windows.

vmdkVMware 3 and 4 compatible image format.

cloopLinux Compressed Loop image, useful only to reuse directly compressed CD-ROM imagespresent for example in the Knoppix CD-ROMs.

24.3. Verifying virtualization extensionsUse this section to determine whether your system has the hardware virtualization extensions.Virtualization extensions (Intel VT or AMD-V) are required for full virtualization.

1. Run the following command to verify the CPU virtualization extensions are available:

$ grep -E 'svm|vmx' /proc/cpuinfo

2. Analyze the output.

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• The following output contains a vmx entry indicating an Intel processor with the Intel VTextensions:

flags : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm syscall lm constant_tsc pni monitor ds_cpl vmx est tm2 cx16 xtpr lahf_lm

• The following output contains an svm entry indicating an AMD processor with the AMD-Vextensions:

flags : fpu tsc msr pae mce cx8 apic mtrr mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext 3dnow pni cx16 lahf_lm cmp_legacy svm cr8legacy ts fid vid ttp tm stc

If any output is received, the processor has the hardware virtualization extensions. However insome circumstances manufacturers disable the virtualization extensions in BIOS.

The "flags:" output content may appear multiple times, once for each hyperthread, core or CPUon the system.

The virtualization extensions may be disabled in the BIOS. If the extensions do not appear or fullvirtualization does not work refer to Procedure 34.1, “Enabling virtualization extensions in BIOS”.

3. For users of the KVM hypervisorIf the kvm package is installed. I As an additional check, verify that the kvm modules are loaded inthe kernel:

# lsmod | grep kvm

If the output includes kvm_intel or kvm_amd then the kvm hardware virtualization modules areloaded and your system meets requirements. sudo

Additional output

If the libvirt package is installed, the virsh command can output a full list of virtualization systemcapabilities. Run virsh capabilities as root to receive the complete list.

24.4. Setting KVM processor affinitiesThis section covers setting processor and processing core affinities with libvirt and KVM guests.

By default, libvirt provisions guests using the hypervisor's default policy. For most hypervisors,the policy is to run guests on any available processing core or CPU. There are times when anexplicit policy may be better, in particular for systems with a NUMA (Non-Uniform Memory Access)architecture. A guest on a NUMA system should be pinned to a processing core so that its memoryallocations are always local to the node it is running on. This avoids cross-node memory transportswhich have less bandwidth and can significantly degrade performance.

On a non-NUMA systems some form of explicit placement across the hosts’ sockets, cores andhyperthreads may be more efficient.


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Identifying CPU and NUMA topologyThe first step in deciding what policy to apply is to determine the host’s memory and CPU topology.The virsh nodeinfo command provides information about how many sockets, cores andhyperthreads there are attached a host.

# virsh nodeinfoCPU model: x86_64CPU(s): 8CPU frequency: 1000 MHzCPU socket(s): 2Core(s) per socket: 4Thread(s) per core: 1NUMA cell(s): 1Memory size: 8179176 kB

This system has eight CPUs, in two sockets, each processor has four cores.

The output shows that that the system has a NUMA architecture. NUMA is more complex and requiresmore data to accurately interpret. Use the virsh capabilities to get additional output data on theCPU configuration.

# virsh capabilities<capabilities> <host> <cpu> <arch>x86_64</arch> </cpu> <migration_features> <live/> <uri_transports> <uri_transport>tcp</uri_transport> </uri_transports> </migration_features> <topology> <cells num='2'> <cell id='0'> <cpus num='4'> <cpu id='0'/> <cpu id='1'/> <cpu id='2'/> <cpu id='3'/> </cpus> </cell> <cell id='1'> <cpus num='4'> <cpu id='4'/> <cpu id='5'/> <cpu id='6'/> <cpu id='7'/> </cpus> </cell> </cells> </topology> <secmodel> <model>selinux</model> <doi>0</doi> </secmodel> </host>

[ Additional XML removed ]

</capabilities>

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The output shows two NUMA nodes (also know as NUMA cells), each containing four logical CPUs(four processing cores). This system has two sockets, therefore it can be inferred that each socket isa separate NUMA node. For a guest with four virtual CPUs, it would be optimal to lock the guest tophysical CPUs 0 to 3, or 4 to 7 to avoid accessing non-local memory, which are significantly slowerthan accessing local memory.

If a guest requires eight virtual CPUs, as each NUMA node only has four physical CPUs, a betterutilization may be obtained by running a pair of four virtual CPU guests and splitting the work betweenthem, rather than using a single 8 CPU guest. Running across multiple NUMA nodes significantlydegrades performance for physical and virtualized tasks.

Decide which NUMA node can run the guestLocking a guest to a particular NUMA node offers no benefit if that node does not have sufficient freememory for that guest. libvirt stores information on the free memory available on each node. Use thevirsh freecell command to display the free memory on all NUMA nodes.

# virsh freecell0: 2203620 kB1: 3354784 kB

If a guest requires 3 GB of RAM allocated, then the guest should be run on NUMA node (cell) 1. Node0 only has 2.2GB free which is probably not sufficient for certain guests.

Lock a guest to a NUMA node or physical CPU setOnce you have determined which node to run the guest on, refer to the capabilities data (the output ofthe virsh capabilities command) about NUMA topology.

1. Extract from the virsh capabilities output.

<topology> <cells num='2'> <cell id='0'> <cpus num='4'> <cpu id='0'/> <cpu id='1'/> <cpu id='2'/> <cpu id='3'/> </cpus> </cell> <cell id='1'> <cpus num='4'> <cpu id='4'/> <cpu id='5'/> <cpu id='6'/> <cpu id='7'/> </cpus> </cell> </cells></topology>

2. Observe that the node 1, <cell id='1'>, has physical CPUs 4 to 7.

3. The guest can be locked to a set of CPUs by appending the cpuset attribute to the configurationfile.

a. While the guest is offline, open the configuration file with virsh edit.


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b. Locate where the guest's virtual CPU count is specified. Find the vcpus element.

<vcpus>4</vcpus>

The guest in this example has four CPUs.

c. Add a cpuset attribute with the CPU numbers for the relevant NUMA cell.

<vcpus cpuset='4-7'>4</vcpus>

4. Save the configuration file and restart the guest.

The guest has been locked to CPUs 4 to 7.

Automatically locking guests to CPUs with virt-installThe virt-install provisioning tool provides a simple way to automatically apply a 'best fit' NUMApolicy when guests are created.

The cpuset option for virt-install can use a CPU set of processors or the parameter auto. Theauto parameter automatically determines the optimal CPU locking using the available NUMA data.

For a NUMA system, use the --cpuset=auto with the virt-install command when creatingnew guests.

Tuning CPU affinity on running guestsThere may be times where modifying CPU affinities on running guests is preferable to rebooting theguest. The virsh vcpuinfo and virsh vcpupin commands can perform CPU affinity changes onrunning guests.

The virsh vcpuinfo command gives up to date information about where each virtual CPU isrunning.

In this example, guest1 is a guest with four virtual CPUs is running on a KVM host.

# virsh vcpuinfo guest1VCPU: 0CPU: 3State: runningCPU time: 0.5sCPU Affinity: yyyyyyyyVCPU: 1CPU: 1State: runningCPU Affinity: yyyyyyyyVCPU: 2CPU: 1State: runningCPU Affinity: yyyyyyyyVCPU: 3CPU: 2State: runningCPU Affinity: yyyyyyyy

The virsh vcpuinfo output (the yyyyyyyy value of CPU Affinity) shows that the guest canpresently run on any CPU.

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To lock the virtual CPUs to the second NUMA node (CPUs four to seven), run the followingcommands.

# virsh vcpupin guest1 0 4# virsh vcpupin guest1 1 5# virsh vcpupin guest1 2 6# virsh vcpupin guest1 3 7

The virsh vcpuinfo command confirms the change in affinity.

# virsh vcpuinfo guest1VCPU: 0CPU: 4State: runningCPU time: 32.2sCPU Affinity: ----y---VCPU: 1CPU: 5State: runningCPU time: 16.9sCPU Affinity: -----y--VCPU: 2CPU: 6State: runningCPU time: 11.9sCPU Affinity: ------y-VCPU: 3CPU: 7State: runningCPU time: 14.6sCPU Affinity: -------y

Information from the KVM processes can also confirm that the guest is now running on the secondNUMA node.

# grep pid /var/run/libvirt/qemu/guest1.xml<domstatus state='running' pid='4907'># grep Cpus_allowed_list /proc/4907/task/*/status/proc/4907/task/4916/status:Cpus_allowed_list: 4/proc/4907/task/4917/status:Cpus_allowed_list: 5/proc/4907/task/4918/status:Cpus_allowed_list: 6/proc/4907/task/4919/status:Cpus_allowed_list: 7</section>

24.5. Generating a new unique MAC addressIn some case you will need to generate a new and unique MAC address for a guest. There is nocommand line tool available to generate a new MAC address at the time of writing. The scriptprovided below can generate a new MAC address for your guests. Save the script to your guest asmacgen.py. Now from that directory you can run the script using ./macgen.py and it will generate anew MAC address. A sample output would look like the following:

$ ./macgen.py 00:16:3e:20:b0:11 #!/usr/bin/python# macgen.py script to generate a MAC address for virtualized guests#import random#def randomMAC():


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mac = [ 0x00, 0x16, 0x3e, random.randint(0x00, 0x7f), random.randint(0x00, 0xff), random.randint(0x00, 0xff) ] return ':'.join(map(lambda x: "%02x" % x, mac))#print randomMAC()

Another method to generate a new MAC for your guestYou can also use the built-in modules of python-virtinst to generate a new MAC address andUUID for use in a guest configuration file:

# echo 'import virtinst.util ; print\ virtinst.util.uuidToString(virtinst.util.randomUUID())' | python# echo 'import virtinst.util ; print virtinst.util.randomMAC()' | python

The script above can also be implemented as a script file as seen below.

#!/usr/bin/env python# -*- mode: python; -*-print ""print "New UUID:"import virtinst.util ; print virtinst.util.uuidToString(virtinst.util.randomUUID())print "New MAC:"import virtinst.util ; print virtinst.util.randomMAC()print ""

24.6. Improving guest response timeVirtualized guests can sometimes be slow to respond with certain workloads and usage patterns.Examples of situations which may cause slow or unresponsive guests:

• Severely overcommitted memory.

• Overcommitted memory with high processor usage

• Other (not qemu-kvm processes) busy or stalled processes on the host.

These types of workload may cause guests to appear slow or unresponsive. Usually, the guestsmemory is eventually fully loaded from swap into the hosts main memory. Once the guest is loaded inmain memory, the guest will preform normally. Note, the process of loading a guest from swap to mainmemory may take several seconds per gigabyte of RAM assigned to the guest depending on the typeof storage used for swap and the performance of the components.

KVM virtualized guests function as Linux processes. Linux processes are not permanently kept inmain memory (physical RAM). The kernel scheduler swaps process memory into virtual memory(swap). Swap, with conventional hard disk drives, is thousands of times slower than main memory inmodern computers. If a guest is inactive for long periods of time, the guest may be placed into swapby the kernel.

KVM virtualized guests processes may be moved to swap regardless of whether memory isovercommitted or overall memory usage.

Using unsafe overcommit levels or overcommitting with swap turned off guest processes or othercritical processes may be killed by the pdflush kernel function. pdflush automatically killsprocesses to keep the system from crashing and to free up memory. Always ensure the host hassufficient swap space when overcommitting memory.

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For more information on overcommitting with KVM, refer to Chapter 20, Overcommitting with KVM.

Warning: turning off swap

Virtual memory allows Linux system to use more memory than there is physical RAM on thesystem. Underused processes are swapped out which allows active processes to use memory,improving memory utilization. Disabling swap reduces memory utilization as all processes arestored in physical RAM.

If swap is turned off, do not overcommit guests. Overcommitting guests without any swap cancause guests or the host system to crash.

Turning off swapSwap usage can be completely turned off to prevent guests from being unresponsive while they aremoved back to main memory. This may improve performance but will expose the system to certainrisks.

The swapoff command can disable all swap partitions and swap files on a system.

# swapoff -a

To make this change permanent, remove swap lines from the /etc/fstab file and restart the hostsystem.

Using SSDs for swapUsing Solid State Drives (SSDs) for swap storage may improve the performance of virtualized guests.

Using RAID arrays, faster disks or separate drives dedicated to swap may also improve performance.

24.7. Very Secure ftpdvsftpd can provide access to installation trees for para-virtualized guests (for example, the RedHat Enterprise Linux repositories) or other data. If you have not installed vsftpd during the serverinstallation you can grab the RPM package from your Server directory of your installation media andinstall it using the rpm -ivh vsftpd*.rpm (note that the RPM package must be in your currentdirectory).

1. To configure vsftpd, edit /etc/passwd using vipw and change the ftp user's home directory tothe directory where you are going to keep the installation trees for your guests. An example entryfor the FTP user would look like the following:

ftp:x:14:50:FTP User:/installtree/:/sbin/nologin

2. Verify that vsftpd is not enabled using the chkconfig --list vsftpd:

$ chkconfig --list vsftpdvsftpd 0:off 1:off 2:off 3:off 4:off 5:off 6:off

3. Run the chkconfig --levels 345 vsftpd on to start vsftpd automatically for run levels 3, 4and 5.


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4. Use the chkconfig --list vsftpd command to verify the vsftpd daemon is enabled tostart during system boot:

$ chkconfig --list vsftpdvsftpd 0:off 1:off 2:off 3:on 4:on 5:on 6:off

5. use the service vsftpd start vsftpd to start the vsftpd service:

$service vsftpd start vsftpdStarting vsftpd for vsftpd: [ OK ]

24.8. Disable SMART disk monitoring for guestsSMART disk monitoring can be safely disabled as virtual disks and the physical storage devices aremanaged by the host.

# service smartd stop# chkconfig --del smartd

24.9. Configuring a VNC ServerTo configure a VNC server use the Remote Desktop application in System > Preferences.Alternatively, you can run the vino-preferences command.

The following steps set up a dedicated VNC server session:

1. Edit the ~/.vnc/xstartup file to start a GNOME session whenever vncserver is started. Thefirst time you run the vncserver script it will ask you for a password you want to use for your VNCsession.

2. A sample xstartup file:

#!/bin/sh# Uncomment the following two lines for normal desktop:# unset SESSION_MANAGER# exec /etc/X11/xinit/xinitrc[ -x /etc/vnc/xstartup ] && exec /etc/vnc/xstartup[ -r $HOME/.Xresources ] && xrdb $HOME/.Xresources#xsetroot -solid grey#vncconfig -iconic &#xterm -geometry 80x24+10+10 -ls -title "$VNCDESKTOP Desktop" &#twm &if test -z "$DBUS_SESSION_BUS_ADDRESS" ; then eval `dbus-launch --sh-syntax –exit-with-session` echo "D-BUS per-session daemon address is: \ $DBUS_SESSION_BUS_ADDRESS"fiexec gnome-session

24.10. Gracefully shutting down guestsInstalling virtualized Red Hat Enterprise Linux 6 guests with the Minimal installation installationoption will not install the acpid package.

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Without the acpid package, the Red Hat Enterprise Linux 6 guest does not shut down when the virshshutdown command is executed. The virsh shutdown command is designed to gracefully shutdown virtualized guests.

Using virsh shutdown is easier and safer for system administration. Without graceful shut downwith the virsh shutdown command a system administrator must log into a virtualized guestmanually or send the Ctrl-Alt-Del key combination to each guest.

Other virtualized operating systems

Other virtualized operating systems may be affected by this issue. The virsh shutdowncommand requires that the guest operating system is configured to handle ACPI shut downrequests. Many operating systems require additional configuration on the guest operating systemto accept ACPI shut down requests.

Procedure 24.1. Workaround for Red Hat Enterprise Linux 61. Install the acpid package

The acpid service listen and processes ACPI requests.

Log into the guest and install the acpid package on the guest:

# yum install acpid

2. Enable the acpid serviceSet the acpid service to start during the guest boot sequence and start the service:

# chkconfig acpid on# service acpid start

The guest is now configured to shut down when the virsh shutdown command is used.

24.11. Virtual machine timer management with libvirtAccurate time keeping on virtualized guests is a key challenge for virtualization platforms. Differenthypervisors attempt to handle the problem of time keeping in a variety of ways. Libvirt provideshypervisor independent configuration settings for time management, using the <clock> and <timer>elements in the domain XML. Note that not all options are supported for all hypervisors. The domainXML can be edited using the virsh edit command. See Editing a guest's configuration file fordetails.

<clock>The clock element is used to determine how the guest clock is synchronized with the host clock. Theclock element has the following attributes:

• offsetDetermines how the guest clock is offset from the host clock. The offset attribute has the followingpossible values:


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Table 24.1. Offset attribute values

Value Description

utc The guest clock will be synchronized to UTCwhen booted.

localtime The guest clock will be synchronized to thehost's configured timezone when booted, if any.

timezone The guest clock will be synchronized to a giventimezone, specified by the timezone attribute.

variable The guest clock will be synchronized to anarbitrary offset from UTC. The delta relativeto UTC is specified in seconds, using theadjustment attribute. The guest is free toadjust the Real Time Clock (RTC) over time andexpect that it will be honored following the nextreboot. This is in contrast to utc mode, whereany RTC adjustments are lost at each reboot.

• timezoneThe timezone to which the guest clock is to be synchronized.

• adjustmentThe delta for guest clock synchronization. In seconds, relative to UTC.

Example 24.1. Always synchronize to UTC

<clock offset="utc" />

Example 24.2. Always synchronize to the host timezone

<clock offset="localtime" />

Example 24.3. Synchronize to an arbitrary timezone

<clock offset="timezone" timezone="Europe/Paris" />

Example 24.4. Synchronize to UTC + arbitrary offset

<clock offset="variable" adjustment="123456" />

<timer>A clock element can have zero or more timer elements as children. The timer element specifies a timesource used for guest clock synchronization. The timer element has the following attributes. Only thename is required, all other attributes are optional.

• nameThe name of the time source to use.

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Table 24.2. name attribute values

Value Description

platform The master virtual time source which may beused to drive the policy of other time sources.

pit Programmable Interval Timer - a timer withperiodic interrupts.

rtc Real Time Clock - a continuously running timerwith periodic interrupts.

hpet High Precision Event Timer - multiple timerswith periodic interrupts.

tsc Time Stamp Counter - counts the number ofticks since reset, no interrupts.

• wallclockSpecifies whether the wallclock should track host or guest time. Only valid for a name value ofplatform or rtc.

Table 24.3. wallclock attribute values

Value Description

host RTC wallclock always tracks host time.

guest RTC wallclock always tracks guest time.

• tickpolicyThe policy used to pass ticks on to the guest.

Table 24.4. tickpolicy attribute values

Value Description

none Continue to deliver at normal rate (i.e. ticks aredelayed).

catchup Deliver at a higher rate to catch up.

merge Ticks merged into one single tick.

discard All missed ticks are discarded.

• frequencyUsed to set a fixed frequency, measured in Hz. This attribute is only relevant for a name value oftsc. All other timers operate at a fixed frequency (pit, rtc), or at a frequency fully controlled bythe guest (hpet).

• modeDetermines how the time source is exposed to the guest. This attribute is only relevant for a namevalue of tsc. All other timers are always emulated.

Table 24.5. mode attribute values

Value Description

auto Native if safe, otherwise emulated.

native Always native.

emulate Always emulate.


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Value Description

paravirt Native + para-virtualized.

• presentUsed to override the default set of timers visible to the guest. For example, to enable or disable theHPET.

Table 24.6. present attribute values

Value Description

yes Force this timer to the visible to the guest.

no Force this timer to not be visible to the guest.

Example 24.5. Clock synchronizing to local time with RTC and PIT timers, and the HPET timerdisabled

<clock mode="localtime"> <timer name="rtc" tickpolicy="catchup" wallclock="guest" /> <timer name="pit" tickpolicy="none" /> <timer name="hpet" present="no" /></clock>

Part V. Virtualization storage topics

Introduction to storageadministration for virtualization

These chapters contain information the storage used in a virtualized environment. The chaptersexplain the concepts of storage pools and volumes, provide detailed configuration procedures andcover other relevant storage topics.

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Storage conceptsThis chapter introduces the concepts used for describing managing storage devices.

Local storageLocal storage is directly attached to the host server. Local storage includes local directories, directlyattached disks, and LVM volume groups on local storage devices.

Networked storageNetworked storage covers storage devices shared over a network using standard protocols.Networked storage includes shared storage devices using Fibre Channel, iSCSI, NFS, GFS2, andSCSI RDMA protocols. Networked storage is a requirement for migrating guest virtualized guestsbetween hosts.

25.1. Storage poolsA storage pool is a file, directory, or storage device managed by libvirt for the purpose of providingstorage to virtualized guests. Storage pools are divided into storage volumes that store virtualizedguest images or are attached to virtualized guests as additional storage.

libvirt uses a directory-based storage pool, the /var/lib/libvirt/images/ directory, as thedefault storage pool. The default storage pool can be changed to another storage pool.

Storage pools can be divided up into volumes or allocated directly to a guest. Volumes of a storagepool can be allocated to virtualized guests. There are two categories of storage pool available:

Local storage poolsLocal storage pools are directly attached to the host server. Local storage pools include localdirectories, directly attached disks, and LVM volume groups on local devices.

Local storage pools are useful for development, testing and small deployments that do not requiremigration or large numbers of virtualized guests. Local storage pools are not suitable for manyproduction environments as local storage pools do not support live migration.

Networked (shared) storage poolsNetworked storage pools covers storage devices shared over a network using standard protocols.

Supported protocols for networked storage pools:

• Fibre Channel-based LUNs

• iSCSI

• NFS

• GFS2

• SCSI RDMA protocols (SCSI RCP), the block export protocol used in Infiniband and 10GbE iWARPadapters.

Networked storage is a requirement for migrating guest virtualized guests between hosts. Networkedstorage pools are managed by libvirt.

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25.2. VolumesStorage pools are divided into storage volumes. Storage volumes are an abstraction of physicalpartitions, LVM logical volumes, file-based disk images and other storage types handled by libvirt.Storage volumes are presented to virtualized guests as local storage devices regardless of theunderlying hardware.

Referencing volumesTo reference a specific volume, three approaches are possible:

The name of the volume and the storage poolA volume may be referred to by name, along with an identifier for the storage pool it belongs in.On the virsh command line, this takes the form --pool storage_pool volume_name.

For example, a volume named firstimage in the guest_images pool.

# virsh vol-info --pool guest_images firstimageName: firstimageType: blockCapacity: 20.00 GBAllocation: 20.00 GB

virsh #

The full path to the storage on the host systemA volume may also be referred to by its full path on the file system. When using this approach, apool identifier does not need to be included.

For example, a volume named secondimage.img, visible to the host system as /images/secondimage.img. The image can be referred to as /images/secondimage.img.

# virsh vol-info /images/secondimage.imgName: secondimage.imgType: fileCapacity: 20.00 GBAllocation: 136.00 KB

The unique volume keyWhen a volume is first created in the virtualization system, a unique identifier is generated andassigned to it. The unique identifier is termed the volume key. The format of this volume key variesupon the storage used.

When used with block based storage such as LVM, the volume key may follow this format:

c3pKz4-qPVc-Xf7M-7WNM-WJc8-qSiz-mtvpGn

When used with file based storage, the volume key may instead be a copy of the full path to thevolume storage.

/images/secondimage.img

For example, a volume with the volume key of Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr:

# virsh vol-info Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr

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Name: firstimageType: blockCapacity: 20.00 GBAllocation: 20.00 GB

virsh provides commands for converting between a volume name, volume path, or volume key:

vol-nameReturns the volume name when provided with a volume path or volume key.

# virsh vol-name /dev/guest_images/firstimage firstimage# virsh vol-name Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr

vol-pathReturns the volume path when provided with a volume key, or a storage pool identifier and volumename.

# virsh vol-path Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr/dev/guest_images/firstimage# virsh vol-path --pool guest_images firstimage/dev/guest_images/firstimage

The vol-key commandReturns the volume key when provided with a volume path, or a storage pool identifier and volumename.

# virsh vol-key /dev/guest_images/firstimageWlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr# virsh vol-key --pool guest_images firstimage Wlvnf7-a4a3-Tlje-lJDa-9eak-PZBv-LoZuUr

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Storage pools

26.1. Creating storage pools

26.1.1. Dedicated storage device-based storage poolsThis section covers dedicating storage devices to virtualized guests.

Security issues with dedicated disks

Guests should not be given write access to whole disks or block devices (for example, /dev/sdb). Use partitions (for example, /dev/sdb1) or LVM volumes.

Guests with full access to a disk device may be able to maliciously access other disk devices thatthey are not assigned due to disks not having access control lists.

26.1.1.1. Creating a dedicated disk storage pool using virshThis procedure creates a new storage pool using a dedicated disk device with the virsh command.

Warning

Dedicating a disk to a storage pool will reformat and erase all data presently stored on the diskdevice. Back up the storage device before commencing the procedure.

1. Create a GPT disk label on the diskThe disk must be relabeled with a GUID Partition Table (GPT) disk label. GPT disk labels allow forcreating a large numbers of partitions, up to 128 partitions, on each device. GPT partition tablescan store partition data for far more partitions than the msdos partition table.

# parted /dev/sdbGNU Parted 2.1Using /dev/sdbWelcome to GNU Parted! Type 'help' to view a list of commands.(parted) mklabel New disk label type? gpt (parted) quit Information: You may need to update /etc/fstab.

#

2. Create the storage pool configuration fileCreate a temporary XML text file containing the storage pool information required for the newdevice.

The file must be in the format shown below, and contain the following fields:

<name>guest_images_disk</name>The name parameter determines the name of the storage pool. This example uses the nameguest_images_disk in the example below.

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<device path='/dev/sdb'/>The device parameter with the path attribute specifies the device path of the storagedevice. This example uses the device /dev/sdb .

<target> <path>/dev</path>The file system target parameter with the path sub-parameter determines the location onthe host file system to attach volumes created with this this storage pool.

For example, sdb1, sdb2, sdb3. Using /dev/, as in the example below, means volumescreated from this storage pool can be accessed as /dev/sdb1, /dev/sdb2, /dev/sdb3.

<format type='gpt'/>The format parameter specifies the partition table type. his example uses the gpt in theexample below, to match the GPT disk label type created in the previous step.

Create the XML file for the storage pool device with a text editor.

Example 26.1. Dedicated storage device storage pool

<pool type='disk'> <name>guest_images_disk</name> <source> <device path='/dev/sdb'/> <format type='gpt'/> </source> <target> <path>/dev</path> </target> </pool>

3. Attach the deviceAdd the storage pool definition using the virsh pool-define command with the XMLconfiguration file created in the previous step.

# virsh pool-define ~/guest_images_disk.xmlPool guest_images_disk defined from /root/guest_images_disk.xml# virsh pool-list --allName State Autostart -----------------------------------------default active yes guest_images_disk inactive no

4. Start the storage poolStart the storage pool with the virsh pool-start command. Verify the pool is started with thevirsh pool-list --all command.

# virsh pool-start guest_images_diskPool guest_images_disk started# virsh pool-list --allName State Autostart -----------------------------------------default active yes guest_images_disk active no

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5. Turn on autostartTurn on autostart for the storage pool. Autostart configures the libvirtd service to start thestorage pool when the service starts.

# virsh pool-autostart guest_images_diskPool guest_images_disk marked as autostarted# virsh pool-list --allName State Autostart -----------------------------------------default active yes guest_images_disk active yes

6. Verify the storage pool configurationVerify the storage pool was created correctly, the sizes reported correctly, and the state reports asrunning.

# virsh pool-info guest_images_diskName: guest_images_diskUUID: 551a67c8-5f2a-012c-3844-df29b167431cState: runningCapacity: 465.76 GBAllocation: 0.00 Available: 465.76 GB# ls -la /dev/sdbbrw-rw----. 1 root disk 8, 16 May 30 14:08 /dev/sdb# virsh vol-list guest_images_diskName Path-----------------------------------------

7. Optional: Remove the temporary configuration fileRemove the temporary storage pool XML configuration file if it is not needed.

# rm ~/guest_images_disk.xml

A dedicated storage device storage pool is now available.

26.1.2. Partition-based storage poolsThis section covers using a pre-formatted block device, a partition, as a storage pool.

For the following examples, a host has a 500GB hard drive (/dev/sdc) partitioned into one 500GB,ext4 formatted partition (/dev/sdc1). We set up a storage pool for it using the procedure below.

26.1.2.1. Creating a partition-based storage pool using virt-managerThis procedure creates a new storage pool using a partition of a storage device.

Procedure 26.1. Creating a partition-based storage pool with virt-manager1. Open the storage pool settings

a. In the virt-manager graphical interface, select the host from the main window.

Open the Edit menu and select Host Details


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b. Click on the Storage tab of the Host Details window.


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2. Create the new storage poola. Add a new pool (part 1)

Press the + button (the add pool button). The Add a New Storage Pool wizard appears.

Choose a Name for the storage pool. This example uses the name guest_images_fs.Change the Type to fs: Pre-Formatted Block Device.


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b. Add a new pool (part 2)Change the Target Path, Format, and Source Path fields.

Target PathEnter the location to mount the source device for the storage pool in the Target Pathfield. If the location does does not already exist, virt-manager will create the directory.

FormatSelect a format from the Format list. The device is formatted with the selected format.

This example uses the ext4 file system, the default Red Hat Enterprise Linux filesystem.

Source PathEnter the device in the Source Path field.

This example uses the /dev/sdc1 device.

Verify the details and press the Finish button to create the storage pool.

3. Verify the new storage poolThe new storage pool appears in the storage list on the left after a few seconds. Verify the size isreported as expected, 458.20 GB Free in this example. Verify the State field reports the newstorage pool as Active.

Select the storage pool. In the Autostart field, click the On Boot checkbox. This will make surethe storage device starts whenever the libvirtd service starts.


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The storage pool is now created, close the Host Details window.

26.1.2.2. Creating a partition-based storage pool using virshThis section covers creating a partition-based storage pool with the virsh command.

Security warning

Do not use this procedure to assign an entire disk as a storage pool (for example, /dev/sdb).Guests should not be given write access to whole disks or block devices. Only use this method toassign partitions (for example, /dev/sdb1) to storage pools.

Procedure 26.2. Creating pre-formatted block device storage pools using virsh1. Create the storage pool definition

Use the virsh pool-define-as command to create a new storage pool definition. There arethree options that must be provided to define a pre-formatted disk as a storage pool:

Partition nameThe name parameter determines the name of the storage pool. This example uses the nameguest_images_fs in the example below.

deviceThe device parameter with the path attribute specifies the device path of the storagedevice. This example uses the partition /dev/sdc1 .

mountpointThe mountpoint on the local file system where the formatted device will be mounted. If themount point directory does not exist, the virsh command can create the directory.


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The directory /guest_images is used in this example.

# virsh pool-define-as guest_images_fs fs - - /dev/sdc1 - "/guest_images"Pool guest_images_fs defined

The new pool and mount points are now created.

2. Verify the new poolList the present storage pools.

# virsh pool-list --allName State Autostart-----------------------------------------default active yesguest_images_fs inactive no

3. Ceate the mount pointUse the virsh pool-build command to create a mount point for a pre-formatted file systemstorage pool.

# virsh pool-build guest_images_fsPool guest_images_fs built# ls -la /guest_imagestotal 8drwx------. 2 root root 4096 May 31 19:38 .dr-xr-xr-x. 25 root root 4096 May 31 19:38 ..# virsh pool-list --allName State Autostart-----------------------------------------default active yesguest_images_fs inactive no

4. Start the storage poolUse the virsh pool-start command to mount the file system onto the mount point and makethe pool available for use.

# virsh pool-start guest_images_fsPool guest_images_fs started# virsh pool-list --allName State Autostart-----------------------------------------default active yesguest_images_fs active no

5. Turn on autostartBy default, a storage pool is defined with virsh is not set to automatically start each time thelibvirtd starts. Turn on automatic start with the virsh pool-autostart command. Thestorage pool is now automatically started each time libvirtd starts.

# virsh pool-autostart guest_images_fsPool guest_images_fs marked as autostarted

# virsh pool-list --allName State Autostart-----------------------------------------default active yes

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guest_images_fs active yes

6. Verify the storage poolVerify the storage pool was created correctly, the sizes reported are as expected, and the state isreported as running. Verify there is a "lost+found" directory in the mount point on the file system,indicating the device is mounted.

# virsh pool-info guest_images_fsName: guest_images_fsUUID: c7466869-e82a-a66c-2187-dc9d6f0877d0State: runningCapacity: 458.39 GBAllocation: 197.91 MBAvailable: 458.20 GB# mount | grep /guest_images/dev/sdc1 on /guest_images type ext4 (rw)# ls -la /guest_imagestotal 24drwxr-xr-x. 3 root root 4096 May 31 19:47 .dr-xr-xr-x. 25 root root 4096 May 31 19:38 ..drwx------. 2 root root 16384 May 31 14:18 lost+found

26.1.3. Directory-based storage poolsThis section covers storing virtualized guests in a directory on the host.

Directory-based storage pools can be created with virt-manager or the virsh command line tools.

26.1.3.1. Creating a directory-based storage pool with virt-manager

1. Create the local directorya. Optional: Create a new directory for the storage pool

Create the directory on the host for the storage pool. An existing directory can be used ifpermissions and SELinux are configured correctly. This example uses a directory named /guest_images.

# mkdir /guest_images

b. Set directory ownershipChange the user and group ownership of the directory. The directory must be owned by theroot user.

# chown root:root /guest_images

c. Set directory permissionsChange the file permissions of the directory.

# chmod 700 /guest_images

d. Verify the changesVerify the permissions were modified. The output shows a correctly configured emptydirectory.

# ls -la /guest_images


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total 8drwx------. 2 root root 4096 May 28 13:57 .dr-xr-xr-x. 26 root root 4096 May 28 13:57 ..

2. Configure SELinux file contextsConfigure the correct SELinux context for the new directory.

# semanage fcontext -a -t virt_image_t /guest_images

3. Open the storage pool settingsa. In the virt-manager graphical interface, select the host from the main window.




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4. Create the new storage poola. Add a new pool (part 1)


Choose a Name for the storage pool. This example uses the name guest_images_dir.Change the Type to dir: Filesystem Directory.


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b. Add a new pool (part 2)Change the Target Path field. This example uses /guest_images.

Verify the details and press the Finish button to create the storage pool.

5. Verify the new storage poolThe new storage pool appears in the storage list on the left after a few seconds. Verify the sizeis reported as expected, 36.41 GB Free in this example. Verify the State field reports the newstorage pool as Active.

Select the storage pool. In the Autostart field, click the On Boot checkbox. This will make surethe storage pool starts whenever the libvirtd service sarts.


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The storage pool is now created, close the Host Details window.

26.1.3.2. Creating a directory-based storage pool with virsh

1. Create the storage pool definitionUse the virsh pool-define-as command to define a new storage pool. There are twooptions required for creating directory-based storage pools:

• The name of the storage pool.

This example uses the name guest_images_dir. All further virsh commands used in thisexample use this name.

• The path to a file system directory for storing virtualized guest image files . If this directorydoes not exist, virsh will create it.

This example uses the /guest_images directory.

# virsh pool-define-as guest_images_dir dir - - - - "/guest_images"Pool guest_images_dir defined

2. Verify the storage pool is listedVerify the storage pool object is created correctly and the state reports it as inactive.

# virsh pool-list --allName State Autostart -----------------------------------------default active yes guest_images_dir inactive no


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3. Create the local directoryUse the virsh pool-build command to build the directory-based storage pool. virsh pool-build sets the required permissions and SELinux settings for the directory and creates thedirectory if it does not exist.

# virsh pool-build guest_images_dirPool guest_images_dir built# ls -la /guest_imagestotal 8drwx------. 2 root root 4096 May 30 02:44 .dr-xr-xr-x. 26 root root 4096 May 30 02:44 ..# virsh pool-list --allName State Autostart -----------------------------------------default active yes guest_images_dir inactive no

4. Start the storage poolUse the virsh command pool-start for this. pool-start enables a directory storage pool,allowing it to be used for volumes and guests.

# virsh pool-start guest_images_dirPool guest_images_dir started# virsh pool-list --allName State Autostart -----------------------------------------default active yes guest_images_dir active no


# virsh pool-autostart guest_images_dirPool guest_images_dir marked as autostarted# virsh pool-list --allName State Autostart -----------------------------------------default active yes guest_images_dir active yes


# virsh pool-info guest_images_dirName: guest_images_dirUUID: 779081bf-7a82-107b-2874-a19a9c51d24cState: runningCapacity: 49.22 GBAllocation: 12.80 GBAvailable: 36.41 GB

# ls -la /guest_imagestotal 8drwx------. 2 root root 4096 May 30 02:44 .dr-xr-xr-x. 26 root root 4096 May 30 02:44 ..#

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A directory-based storage pool is now available.

26.1.4. LVM-based storage poolsThis chapter covers using LVM volume groups as storage pools.

LVM-based storage groups provide flexibility of

Warning

LVM-based storage pools require a full disk partition. This partition will be formatted and alldata presently stored on the disk device will be erased. Back up the storage device beforecommencing the procedure.

26.1.4.1. Creating an LVM-based storage pool with virt-managerLVM-based storage pools can use existing LVM volume groups or create new LVM volume groups ona blank partition.

1. Optional: Create new partition for LVM volumesThese steps describe how to create a new partition and LVM volume group on a new hard diskdrive.

Warning

This procedure will remove all data from the selected storage device.

a. Create a new partitionUse the fdisk command to create a new disk partition from the command line. The followingexample creates a new partition that uses the entire disk on the storage device /dev/sdb.

# fdisk /dev/sdbCommand (m for help):

Press n for a new partition.

b. Press p for a primary partition.

Command action e extended p primary partition (1-4)

c. Choose an available partition number. In this example the first partition is chosen by entering1.

Partition number (1-4): 1

d. Enter the default first cylinder by pressing Enter.

First cylinder (1-400, default 1):


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e. Select the size of the partition. In this example the entire disk is allocated by pressing Enter.

Last cylinder or +size or +sizeM or +sizeK (2-400, default 400):

f. Set the type of partition by pressing t.

Command (m for help): t

g. Choose the partition you created in the previous steps. In this example, the partition numberis 1.


h. Enter 8e for a Linux LVM partition.

Hex code (type L to list codes): 8e

i. write changes to disk and quit.

Command (m for help): w Command (m for help): q

j. Create a new LVM volume groupCreate a new LVM volume group with the vgcreate command. This example creates avolume group named guest_images_lvm.

# vgcreate guest_images_lvm /dev/sdb1 Physical volmue "/dev/vdb1" successfully created Volume group "guest_images_lvm" successfully created

The new LVM volume group, guest_images_lvm, can now be used for an LVM-based storagepool.

2. Open the storage pool settingsa. In the virt-manager graphical interface, select the host from the main window.



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3. Create the new storage poola. Start the Wizard


Choose a Name for the storage pool. We use guest_images_lvm for this example. Thenchange the Type to logical: LVM Volume Group, and


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b. Add a new pool (part 2)Change the Target Path field. This example uses /guest_images.

Now fill in the Target Path and Source Path fields, then tick the Build Pool check box.

• Use the Target Path field to either select an existing LVM volume group or as the name fora new volume group. The default format is /dev/storage_pool_name.

This example uses a new volume group named /dev/guest_images_lvm.

• The Source Path field is optional if an existing LVM volume group is used in the TargetPath.

For new LVM volume groups, input the location of a storage device in the Source Pathfield. This example uses a blank partition /dev/sdc.

• The Build Pool checkbox instructs virt-manager to create a new LVM volume group. Ifyou are using an existing volume group you should not select the Build Pool checkbox.

This example is using a blank partition to create a new volume group so the Build Poolcheckbox must be selected.

Verify the details and press the Finish button format the LVM volume group and create thestorage pool.

c. Confirm the device to be formattedA warning message appears.


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Press the Yes button to proceed to erase all data on the storage device and create thestorage pool.

4. Verify the new storage poolThe new storage pool will appear in the list on the left after a few seconds. Verify the details arewhat you expect, 465.76 GB Free in our example. Also verify the State field reports the newstorage pool as Active.

It is generally a good idea to have the Autostart check box enabled, to ensure the storage poolstarts automatically with libvirtd.

Close the Host Details dialog, as the task is now complete.

26.1.4.2. Creating an LVM-based storage pool with virsh•

# virsh pool-define-as guest_images_lvm logical - - /dev/sdc libvirt_lvm /dev/libvirt_lvm

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Pool guest_images_lvm defined# virsh pool-build guest_images_lvmPool guest_images_lvm built# virsh pool-start guest_images_lvmPool guest_images_lvm started# vgsVG #PV #LV #SN Attr VSize VFree libvirt_lvm 1 0 0 wz--n- 465.76g 465.76g# virsh pool-autostart guest_images_lvmPool guest_images_lvm marked as autostarted

# virsh pool-list --allName State Autostart -----------------------------------------default active yes guest_images_lvm active yes

# virsh vol-create-as guest_images_lvm volume1 8GVol volume1 created



# virsh vol-list guest_images_lvmName Path-----------------------------------------volume1 /dev/libvirt_lvm/volume1volume2 /dev/libvirt_lvm/volume2volume3 /dev/libvirt_lvm/volume3

# lvscanACTIVE '/dev/libvirt_lvm/volume1' [8.00 GiB] inheritACTIVE '/dev/libvirt_lvm/volume2' [8.00 GiB] inheritACTIVE '/dev/libvirt_lvm/volume3' [8.00 GiB] inherit# lvsLV VG Attr LSize Origin Snap% Move Log Copy% Convertvolume1 libvirt_lvm -wi-a- 8.00gvolume2 libvirt_lvm -wi-a- 8.00gvolume3 libvirt_lvm -wi-a- 8.00g# vgsVG #PV #LV #SN Attr VSize VFreelibvirt_lvm 1 3 0 wz--n- 465.76g 441.76gvg_host2 1 3 0 wz--n- 465.27g 0#

26.1.5. iSCSI-based storage poolsThis section covers using iSCSI-based devices to store virtualized guests.

iSCSI (Internet Small Computer System Interface) is a network protocol for sharing storage devices.iSCSI connects initiators (storage clients) to targets (storage servers) using SCSI instructions over theIP layer. For more information and background on the iSCSI protocol refer to wikipedia's iSCSI article1.

26.1.5.1. Configuring a software iSCSI targetThe scsi-target-utils package provides a tool for creating software-backed iSCSI targets.

1 http://en.wikipedia.org/wiki/ISCSI

http://en.wikipedia.org/wiki/ISCSI

http://en.wikipedia.org/wiki/ISCSI


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Procedure 26.3. Creating an iSCSI target1. Install the required packages

Install the scsi-target-utils package and all dependencies

# yum install scsi-target-utils

2. Start the tgtd serviceThe tgtd service hosts SCSI targets and uses the iSCSI protocol to host targets. Start the tgtdservice and make the service persistent after restarting with the chkconfig command.

# service tgtd start# chkconfig tgtd on

3. Optional: Create LVM volumesLVM volumes are useful for iSCSI backing images. LVM snapshots and resizing can be beneficialfor virtualized guests. This example creates an LVM image named virtimage1 on a new volumegroup named virtstore on a RAID5 array for hosting virtualized guests with iSCSI.

a. Create the RAID arrayCreating software RAID5 arrays is covered by the Red Hat Enterprise Linux DeploymentGuide.

b. Create the LVM volume groupCreate a volume group named virtstore with the vgcreate command.

# vgcreate virtstore /dev/md1

c. Create a LVM logical volumeCreate a logical volume group named virtimage1 on the virtstore volume group with asize of 20GB using the lvcreate command.

# lvcreate --size 20G -n virtimage1 virtstore

The new logical volume, virtimage1, is ready to use for iSCSI.

4. Optional: Create file-based imagesFile-based storage is sufficient for testing but is not recommended for production environmentsor any significant I/O activity. This optional procedure creates a file based imaged namedvirtimage2.img for an iSCSI target.

a. Create a new directory for the imageCreate a new directory to store the image. The directory must have the correct SELinuxcontexts.

# mkdir -p /var/lib/tgtd/virtualization

b. Create the image fileCreate an image named virtimage2.img with a size of 10GB.

# dd if=/dev/zero of=/var/lib/tgtd/virtualization/virtimage2.img bs=1M seek=10000 count=0


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c. Configure SELinux file contextsConfigure the correct SELinux context for the new image and directory.

# restorecon -R /var/lib/tgtd

The new file-based image, virtimage2.img, is ready to use for iSCSI.

5. Create targetsTargets can be created by adding a XML entry to the /etc/tgt/targets.conf file. Thetarget attribute requires an iSCSI Qualified Name (IQN). The IQN is in the format:

iqn.yyyy-mm.reversed domain name:optional identifier text

Where:

• yyyy-mm represents the year and month the device was started (for example: 2010-05);

• reversed domain name is the hosts domain name in reverse (for exampleserver1.example.com in an IQN would be com.example.server1); and

• optional identifier text is any text string, without spaces, that assists the administratorin identifying devices or hardware.

This example creates iSCSI targets for the two types of images created in the optional steps onserver1.example.com with an optional identifier trial. Add the following to the /etc/tgt/targets.conf file.

<target iqn.2010-05.com.example.server1:trial>backing-store /dev/virtstore/virtimage1 #LUN 1backing-store /var/lib/tgtd/virtualization/virtimage2.img #LUN 2write-cache off</target>

Ensure that the /etc/tgt/targets.conf file contains the default-driver iscsi line toset the driver type as iSCSI. The driver uses iSCSI by default.

Important

This example creates a globally accessible target without access control. Refer to the scsi-target-utils for information on implementing secure access.

6. Restart the tgtd serviceRestart the tgtd service to reload the configuration changes.

# service tgtd restart

7. iptables configurationOpen port 3260 for iSCSI access with iptables.

# iptables -I INPUT -p tcp -m tcp --dport 3260 -j ACCEPT# service iptables save


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# service iptables restart

8. Verify the new targetsView the new targets to ensure the setup was success with the tgt-admin --show command.

# tgt-admin --showTarget 1: iqn.2010-05.com.example.server1:trialSystem information:Driver: iscsiState: readyI_T nexus information:LUN information:LUN: 0 Type: controller SCSI ID: IET 00010000 SCSI SN: beaf10 Size: 0 MB Online: Yes Removable media: No Backing store type: rdwr Backing store path: NoneLUN: 1 Type: disk SCSI ID: IET 00010001 SCSI SN: beaf11 Size: 20000 MB Online: Yes Removable media: No Backing store type: rdwr Backing store path: /dev/virtstore/virtimage1LUN: 2 Type: disk SCSI ID: IET 00010002 SCSI SN: beaf12 Size: 10000 MB Online: Yes Removable media: No Backing store type: rdwr Backing store path: /var/lib/tgtd/virtualization/virtimage2.imgAccount information:ACL information:ALL

Security warning

The ACL list is set to all. This allows all systems on the local network to access this device. Itis recommended to set host access ACLs for production environments.

9. Optional: Test discoveryTest whether the new iSCSI device is discoverable.

# iscsiadm --mode discovery --type sendtargets --portal server1.example.com127.0.0.1:3260,1 iqn.2010-05.com.example.server1:trial1

10. Optional: Test attaching the deviceAttach the new device (iqn.2010-05.com.example.server1:trial1) to determine whetherthe device can be attached.


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# iscsiadm -d2 -m node --loginscsiadm: Max file limits 1024 1024

Logging in to [iface: default, target: iqn.2010-05.com.example.server1:trial1, portal: 10.0.0.1,3260]Login to [iface: default, target: iqn.2010-05.com.example.server1:trial1, portal: 10.0.0.1,3260] successful.

Detach the device.

# iscsiadm -d2 -m node --logoutscsiadm: Max file limits 1024 1024

Logging out of session [sid: 2, target: iqn.2010-05.com.example.server1:trial1, portal: 10.0.0.1,3260Logout of [sid: 2, target: iqn.2010-05.com.example.server1:trial1, portal: 10.0.0.1,3260] successful.

An iSCSI device is now ready to use for virtualization.

26.1.5.2. Adding an iSCSI target to virt-managerThis procedure covers creating a storage pool with an iSCSI target in virt-manager.

Procedure 26.4. Adding an iSCSI device to virt-manager1. Open the host storage tab

Open the Storage tab in the Host Details window.

a. Open virt-manager.

b. Select a host from the main virt-manager window.


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c. Open the Edit menu and select Host Details.

d. Click on the Storage tab of the Host Details window.


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2. Add a new pool (part 1)Press the + button (the add pool button). The Add a New Storage Pool wizard appears.

Choose a name for the storage pool, change the Type to iscsi, and press Forward to continue.


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3. Add a new pool (part 2)Enter the target path for the device, the host name of the target and the source path (the IQN).The Format option is not available as formatting is handled by the guests. It is not advised to editthe Target Path. The default target path value, /dev/disk/by-path/, adds the drive path tothat folder. The target path should be the same on all hosts for migration.

Enter the hostname or IP address of the iSCSI target. This example usesserver1.example.com.

Enter the source path, the IQN for the iSCSI target. This example usesiqn.2010-05.com.example.server1:trial1.

Press Finish to create the new storage pool.

26.1.5.3. Creating an iSCSI-based storage pool with virsh

1. Create the storage pool definitionThe example below is an XML definition file for a iSCSI-based storage pool.

<name>trial1</name>The name element sets the name for the storage pool. The name is required and must beunique.

<uuid>afcc5367-6770-e151-bcb3-847bc36c5e28</uuid>The optional uuid element provides a unique global identifier for the storage pool. The uuidelement can contain any valid UUID or an existing UUID for the storage device. If a UUID isnot provided, virsh will generate a UUID for the storage pool.

<host name='server1.example.com'/>The host element with the name attribute specifies the hostname of the iSCSI server. Thehost element attribute can contain a port attribute for a non-standard iSCSI protocol portnumber.


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<device path='iqn.2010-05.com.example.server1:trial1'/>The device element path attribute must contain the IQN for the iSCSI server.

With a text editor, create an XML file for the iSCSI storage pool. This example uses a XMLdefinition named trial1.xml.

<pool type='iscsi'> <name>trial1</name> <uuid>afcc5367-6770-e151-bcb3-847bc36c5e28</uuid> <source> <host name='server1.example.com'/> <device path='iqn.2010-05.com.example.server1:trial1'/> </source> <target> <path>/dev/disk/by-path</path> </target></pool>

Use the pool-define command to define the storage pool but not start it.

# virsh pool-define trial1.xmlPool trial1 defined

2. Alternative step: Use pool-define-as to define the pool from the command lineStorage pool definitions can be created with the virsh command line tool. Creating storage poolswith virsh is useful for systems administrators using scripts to create multiple storage pools.

The virsh pool-define-as command has several parameters which are accepted in thefollowing format:

virsh pool-define-as name type source-host source-path source-dev source-name target

The type, iscsi, defines this pool as an iSCSI based storage pool. The name parameter mustbe unique and sets the name for the storage pool. The source-host and source-pathparameters are the hostname and iSCSI IQN respectively. The source-dev and source-nameparameters are not required for iSCSI-based pools, use a - character to leave the field blank. Thetarget parameter defines the location for mounting the iSCSI device on the host.

The example below creates the same iSCSI-based storage pool as the previous step.

# virsh pool-define-as trial1 iscsi server1.example.com iqn.2010-05.com.example.server1:trial1 - - /dev/disk/by-pathPool trial1 defined

3. Verify the storage pool is listedVerify the storage pool object is created correctly and the state reports as inactive.

# virsh pool-list --allName State Autostart -----------------------------------------default active yes trial1 inactive no


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4. Start the storage poolUse the virsh command pool-start for this. pool-start enables a directory storage pool,allowing it to be used for volumes and guests.

# virsh pool-start guest_images_diskPool guest_images_disk started# virsh pool-list --allName State Autostart -----------------------------------------default active yes trial1 active no


# virsh pool-autostart trial1Pool trial1 marked as autostarted

Verify that the trial1 pool has autostart set:

# virsh pool-list --allName State Autostart -----------------------------------------default active yes trial1 active yes


# virsh pool-info trial1Name: trial1UUID: afcc5367-6770-e151-bcb3-847bc36c5e28State: runningPersistent: unknownAutostart: yesCapacity: 100.31 GBAllocation: 0.00Available: 100.31 GB

An iSCSI-based storage pool is now available.

26.1.6. NFS-based storage poolsThis procedure covers creating a storage pool with a NFS mount point in virt-manager.

26.1.6.1. Creating a NFS-based storage pool with virt-manager

1. Open the host storage tabOpen the Storage tab in the Host Details window.

a. Open virt-manager.

b. Select a host from the main virt-manager window.

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c. Open the Edit menu and select Host Details.

d. Click on the Storage tab of the Host Details window.


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2. Create a new pool (part 1)Press the + button (the add pool button). The Add a New Storage Pool wizard appears.

Choose a name for the storage pool and press Forward to continue.

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3. Create a new pool (part 2)Enter the target path for the device, the hostname and the NFS share path. Set the Format optionto NFS or auto (to detect the type). The target path must be identical on all hosts for migration.

Enter the hostname or IP address of the NFS server. This example usesserver1.example.com.

Enter the NFS path. This example uses /nfstrial.

Press Finish to create the new storage pool.

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Volumes

27.1. Creating volumesThis section shows how to create disk volumes inside a block based storage pool.

# virsh vol-create-as guest_images_disk volume1 8GVol volume1 created



# virsh vol-list guest_images_diskName Path-----------------------------------------volume1 /dev/sdb1volume2 /dev/sdb2volume3 /dev/sdb3

# parted -s /dev/sdb printModel: ATA ST3500418AS (scsi)Disk /dev/sdb: 500GBSector size (logical/physical): 512B/512BPartition Table: gpt

Number Start End Size File system Name Flags2 17.4kB 8590MB 8590MB primary3 8590MB 17.2GB 8590MB primary1 21.5GB 30.1GB 8590MB primary

#

27.2. Cloning volumesPlaceholder : Needs to describe what "cloning" means in this regard

The new volume will be allocated from storage in the same storage pool as the volume being cloned.

# virsh vol-clone --pool guest_images_disk volume3 clone1Vol clone1 cloned from volume3

# virsh vol-list guest_images_diskName Path -----------------------------------------clone1 /dev/sdb1 volume2 /dev/sdb2 volume3 /dev/sdb3


Number Start End Size File system Name Flags2 8590MB 17.2GB 8590MB primary3 17.2GB 25.8GB 8590MB primary1 25.8GB 34.4GB 8590MB primary

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#

27.3. Adding storage devices to guestsThis section covers adding storage devices to a virtualized guest. Additional storage can only beadded after guests are created.

27.3.1. Adding file based storage to a guestFile-based storage or file-based containers are files on the hosts file system which act as virtualizedhard drives for virtualized guests. To add a file-based container perform the following steps:

1. Create an empty container file or using an existing file container (such as an ISO file).

a. Create a sparse file using the dd command. Sparse files are not recommended due to dataintegrity and performance issues. Sparse files are created much faster and can used fortesting but should not be used in production environments.

# dd if=/dev/zero of=/var/lib/libvirt/images/FileName.img bs=1M seek=4096 count=0

b. Non-sparse, pre-allocated files are recommended for file-based storage images. Create anon-sparse file, execute:

# dd if=/dev/zero of=/var/lib/libvirt/images/FileName.img bs=1M count=4096

Both commands create a 400MB file which can be used as additional storage for a virtualizedguest.

2. Dump the configuration for the guest. In this example the guest is called Guest1 and the file issaved in the users home directory.

# virsh dumpxml Guest1 > ~/Guest1.xml

3. Open the configuration file (Guest1.xml in this example) in a text editor. Find the <disk>elements, these elements describe storage devices. The following is an example disk element:

<disk type='file' device='disk'> <driver name='virtio' cache='none'/> <source file='/var/lib/libvirt/images/Guest1.img'/> <target dev='sda'/></disk>

4. Add the additional storage by duplicating or writing a new <disk> element. Ensure you specifya device name for the virtual block device attributes. These attributes must be unique for eachguest configuration file. The following example is a configuration file section which contains anadditional file-based storage container named FileName.img.

<disk type='file' device='disk'> <driver name='virtio' cache='none'/> <source file='/var/lib/libvirt/images/Guest1.img'/> <target dev='sda'/></disk><disk type='file' device='disk'> <driver name='virtio' cache='none'/>

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<source file='/var/lib/libvirt/images/FileName.img'/> <target dev='sdb'/></disk>

5. Restart the guest from the updated configuration file.

# virsh create Guest1.xml

6. The following steps are Linux guest specific. Other operating systems handle new storagedevices in different ways. For other systems, refer to that operating system's documentation

The guest now uses the file FileName.img as the device called /dev/sdb. This device requiresformatting from the guest. On the guest, partition the device into one primary partition for theentire device then format the device.

a. Press n for a new partition.

# fdisk /dev/sdbCommand (m for help):

b. Press p for a primary partition.

Command actione extendedp primary partition (1-4)

c. Choose an available partition number. In this example the first partition is chosen by entering1.


d. Enter the default first cylinder by pressing Enter.

First cylinder (1-400, default 1):

e. Select the size of the partition. In this example the entire disk is allocated by pressing Enter.

Last cylinder or +size or +sizeM or +sizeK (2-400, default 400):

f. Set the type of partition by pressing t.

Command (m for help): t

g. Choose the partition you created in the previous steps. In this example, the partition numberis 1.


h. Enter 83 for a linux partition.

Hex code (type L to list codes): 83

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i. write changes to disk and quit.

Command (m for help): w Command (m for help): q

j. Format the new partition with the ext3 file system.

# mke2fs -j /dev/sdb1

7. Mount the disk on the guest.

# mount /dev/sdb1 /myfiles

The guest now has an additional virtualized file-based storage device.

27.3.2. Adding hard drives and other block devices to a guestSystem administrators use additional hard drives to provide increased storage space for a guest, or toseparate system data from user data.

Procedure 27.1. Adding physical block devices to virtualized guestsThis procedure describes how to add a hard drive on the host to a virtualized guest. It applies to allphysical block devices, including CD-ROM, DVD and floppy devices.

1. Physically attach the hard disk device to the host. Configure the host if the drive is not accessibleby default.

2. Configure the device with multipath and persistence on the host if required.

3. Use the virsh attach command as below, replacing:

# virsh attach-disk myguest /dev/sdb1 sdc --driver tap --mode readonly

• myguest with the name of the guest.

• /dev/sdb1 with the device on the host to add.

• sdc with the location on the guest where the device should be added. It must be an unuseddevice name.

Use the sd* notation for Windows guests as well, the guest will recognize the device correctly.

• Only include the --mode readonly parameter if the device should be read only to the guest.

Additionally, there are optional arguments that may be added:

• Append the --type hdd parameter to the command for CD-ROM or DVD devices.

• Append the --type floppy parameter to the command for floppy devices.

4. The guest now has a new hard disk device called /dev/sdb on Linux or D: drive, or similar,on Windows. This device may require formatting.

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Block device security - disk labels

The host should not use disk labels to identify file systems in the fstab file, the initrd file oron the kernel command line. Doing so presents a security risk if less privileged users, such asvirtualized guests, have write access to whole partitions or LVM volumes.

A virtualized guest could write a disk label belonging to the host, to its own block device storage.Upon reboot of the host, the host could then mistakenly use the virtualized guests disk as asystem disk, compromising the host system.

Block device security - whole disk access

Guests should not be given write access to whole disks or block devices (for example, /dev/sdb). Virtualized guests with access to block devices may be able to access other block deviceson the system or modify volume labels which can be used to compromise the host system. Usepartitions (for example, /dev/sdb1) or LVM volumes to prevent this issue.

27.4. Deleting and removing volumesThis section shows how to delete a disk volume from a block based storage pool.

# virsh vol-delete --pool guest_images_disk volume1Vol volume1 deleted

# virsh vol-list guest_images_diskName Path -----------------------------------------volume2 /dev/sdb2 volume3 /dev/sdb3


Number Start End Size File system Name Flags2 8590MB 17.2GB 8590MB primary3 17.2GB 25.8GB 8590MB primary

#

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Miscellaneous storage topics

28.1. Creating a virtualized floppy disk controllerFloppy disk controllers are required for a number of older operating systems, especially for installingdrivers. Presently, physical floppy disk devices cannot be accessed from virtualized guests. However,creating and accessing floppy disk images from virtualized floppy drives should work. This sectioncovers creating a virtualized floppy device.

An image file of a floppy disk is required. Create floppy disk image files with the dd command.Replace /dev/fd0 with the name of a floppy device and name the disk appropriately.

# dd if=/dev/fd0 of=~/legacydrivers.img

This example uses a guest created with virt-manager running a fully virtualized Fedora installationwith an image located in /var/lib/libvirt/images/Fedora.img.

1. Create the XML configuration file for your guest image using the virsh command on a runningguest.

# virsh dumpxml Fedora > Fedora.xml

This saves the configuration settings as an XML file which can be edited to customize theoperations and devices used by the guest. For more information on using the virsh XMLconfiguration files, refer to Chapter 33, Creating custom libvirt scripts.

2. Create a floppy disk image for the guest.

# dd if=/dev/zero of=/var/lib/libvirt/images/Fedora-floppy.img bs=512 count=2880

3. Add the content below, changing where appropriate, to your guest's configuration XML file. Thisexample is an emulated floppy device using a file-based image.

<disk type='file' device='floppy'> <source file='/var/lib/libvirt/images/Fedora-floppy.img'/> <target dev='fda'/></disk>

4. Force the guest to stop. To shut down the guest gracefully, use the virsh shutdown commandinstead.

# virsh destroy Fedora

5. Restart the guest using the XML configuration file.

# virsh create Fedora.xml

The floppy device is now available in the guest and stored as an image file on the host.

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28.2. Configuring persistent storage in Red Hat EnterpriseLinux 6This section is for systems with external or networked storage; for example, Fibre Channel, iSCSI,or SRP based storage devices. It is recommended that those systems have persistent device namesconfigured for your hosts. This assists live migration as well as providing consistent device names andstorage for multiple virtualized systems.

Universally Unique Identifiers (UUIDs) are a standardized method for identifying computers anddevices in distributed computing environments. This section uses UUIDs to identify iSCSI, SRP, orFibre Channel LUNs. UUIDs persist after restarts, disconnection and device swaps. The UUID issimilar to a label on the device.

Systems which are not running multipath must use Single path configuration. Systems runningmultipath can use Multiple path configuration.

Single path configurationThis procedure implements LUN device persistence using udev. Only use this procedure for hostswhich are not using multipath.

1. Edit the /etc/scsi_id.config file.

• Add the following line:

options=--whitelisted --replace-whitespace

This sets the default options for scsi_id, ensuring returned UUIDs contains no spaces. TheIET iSCSI target otherwise returns spaces in UUIDs, which can cause problems.

2. To display the UUID for a given device run the scsi_id --whitelisted --replace-whitespace --device=/dev/sd* command. For example:

# scsi_id --whitelisted --replace-whitespace --device=/dev/sdc1IET_00010001

The output may vary from the example above. The output in this example displays the UUID ofthe device /dev/sdc.

3. Verify the UUID output from the scsi_id --whitelisted --replace-whitespace --device=/dev/sd* command is correct and as expected.

4. Create a rule to name the device. Create a file named 20-names.rules in the /etc/udev/rules.d directory. Add new rules to this file. All rules are added to the same file using the sameformat. Rules follow this format:

KERNEL=="sd*", SUBSYSTEM=="block", PROGRAM="/sbin/scsi_id --whitelisted --replace-whitespace /dev/$name", RESULT=="UUID", NAME="devicename"

Replace UUID and devicename with the UUID retrieved above, and a name for the device. Thisis an example for the rule above for three example iSCSI luns:

KERNEL=="sd*", SUBSYSTEM=="block", PROGRAM="/sbin/scsi_id --whitelisted --replace-whitespace /dev/$name", RESULT=="1IET_00010001", NAME="rack4row16lun1"KERNEL=="sd*", SUBSYSTEM=="block", PROGRAM="/sbin/scsi_id --whitelisted --replace-whitespace /dev/$name", RESULT=="1IET_00010002", NAME="rack4row16lun2"

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KERNEL=="sd*", SUBSYSTEM=="block", PROGRAM="/sbin/scsi_id --whitelisted --replace-whitespace /dev/$name", RESULT=="1IET_00010003", NAME="rack4row16lun3"

The udev daemon now searches all devices named /dev/sd* for a matching UUID in the rules.When a matching device is connected to the system the device is assigned the name from therule. For example:

# ls -la /dev/rack4row16*brw-rw---- 1 root disk 8, 18 May 25 23:35 /dev/rack4row16lun1brw-rw---- 1 root disk 8, 34 May 25 23:35 /dev/rack4row16lun2brw-rw---- 1 root disk 8, 50 May 25 23:35 /dev/rack4row16lun3

5. Copy the changes in /etc/scsi_id.config and /etc/udev/rules.d/20-names.rules toall relevant hosts.

Networked storage devices with configured rules now have persistent names on all hosts where thefiles were updated This means you can migrate guests between hosts using the shared storage andthe guests can access the storage devices in their configuration files.

Multiple path configurationThe multipath package is used for systems with more than one physical path from the computerto storage devices. multipath provides fault tolerance, fail-over and enhanced performance fornetwork storage devices attached to Red Hat Enterprise Linux 6 systems.

Implementing LUN persistence in a multipath environment requires defined alias names for yourmultipath devices. Each storage device has a UUID, also known as a World Wide Identifier or WWID,which acts as a key for the aliased names.

This procedure implements LUN device persistence using the multipath daemon.

1. Determine the World Wide Identifier of each device using the scsi_id --whitelisted --replace-whitespace --device=/dev/sd* command:

# scsi_id --whitelisted --replace-whitespace --device=/dev/sde1IET_00010004# scsi_id --whitelisted --replace-whitespace --device=/dev/sdf1IET_00010005# scsi_id --whitelisted --replace-whitespace --device=/dev/sdg1IET_00010006# scsi_id --whitelisted --replace-whitespace --device=/dev/sdh1IET_00010007

2. Create the multipath configuration file, /etc/multipath.conf. In it create a defaultssection, and disable the user_friendly_names option unless you have a specific need for it.It is also a good idea to configure the default arguments for the getuid_callout option. This isgenerally a useful start:

defaults { user_friendly_names no getuid_callout "/sbin/scsi_id --whitelisted --replace-whitespace --device=/dev/%n"}

3. Below the defaults section add a multipaths section (note the plural spelling). In this sectionadd each of the WWIDs identified from the scsi_id command above. For example:

multipaths {


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multipath { wwid 1IET_00010004 alias oramp1 }



multipath { wwid 1IET_00010007 alias oramp4 }}

Multipath devices are created in the /dev/mapper directory. The above example will create 4LUNs named /dev/mapper/oramp1, /dev/mapper/oramp2, /dev/mapper/oramp3 and /dev/mapper/oramp4.

4. Enable the multipathd daemon to start at system boot.

# chkconfig multipathd on# chkconfig --list multipathdmultipathd 0:off 1:off 2:on 3:on 4:on 5:on 6:off

5. The mapping of these device WWIDs to their alias names will now persist across reboots. Forexample:

# ls -la /dev/mapper/oramp*brw-rw---- 1 root disk 253, 6 May 26 00:17 /dev/mapper/oramp1brw-rw---- 1 root disk 253, 7 May 26 00:17 /dev/mapper/oramp2brw-rw---- 1 root disk 253, 8 May 26 00:17 /dev/mapper/oramp3brw-rw---- 1 root disk 253, 9 May 26 00:17 /dev/mapper/oramp4# multipath -lloramp1 (1IET_00010004) dm-6 IET,VIRTUAL-DISKsize=20.0G features='0' hwhandler='0' wp=rw|-+- policy='round-robin 0' prio=1 status=active| `- 8:0:0:4 sde 8:64 active ready running`-+- policy='round-robin 0' prio=1 status=enabled `- 9:0:0:4 sdbl 67:240 active ready runningoramp3 (1IET_00010006) dm-8 IET,VIRTUAL-DISKsize=20.0G features='0' hwhandler='0' wp=rw|-+- policy='round-robin 0' prio=1 status=active| `- 8:0:0:6 sdg 8:96 active ready running`-+- policy='round-robin 0' prio=1 status=enabled `- 9:0:0:6 sdbn 68:16 active ready runningoramp2 (1IET_00010005) dm-7 IET,VIRTUAL-DISKsize=20.0G features='0' hwhandler='0' wp=rw|-+- policy='round-robin 0' prio=1 status=active| `- 8:0:0:5 sdf 8:80 active ready running`-+- policy='round-robin 0' prio=1 status=enabled `- 9:0:0:5 sdbm 68:0 active ready runningoramp4 (1IET_00010007) dm-9 IET,VIRTUAL-DISKsize=20.0G features='0' hwhandler='0' wp=rw|-+- policy='round-robin 0' prio=1 status=active| `- 8:0:0:7 sdh 8:112 active ready running`-+- policy='round-robin 0' prio=1 status=enabled

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`- 9:0:0:7 sdbo 68:32 active ready running

28.3. Accessing data from a guest disk imageThere are various methods for accessing the data from guest image files. One common method is touse the kpartx tool, covered by this section, to mount the guest file system as a loop device whichcan then be accessed.

The kpartx command creates device maps from partition tables. Each guest storage image has apartition table embedded in the file.

The libguestfs and guestfish packages, available from the EPEL1 repository, allow advancedmodification and access to guest file systems. The libguestfs and guestfish packages are not coveredin this section at this time.

Warning

Guests must be offline before their files can be read. Editing or reading files of an active guest isnot possible and may cause data loss or damage.

Procedure 28.1. Accessing guest image data1. Install the kpartx package.

# yum install kpartx

2. Use kpartx to list partition device mappings attached to a file-based storage image. This exampleuses a image file named guest1.img.

# kpartx -l /var/lib/libvirt/images/guest1.imgloop0p1 : 0 409600 /dev/loop0 63loop0p2 : 0 10064717 /dev/loop0 409663

guest1 is a Linux guest. The first partition is the boot partition and the second partition is anEXT3 containing the root partition.

3. Add the partition mappings to the recognized devices in /dev/mapper/.

# kpartx -a /var/lib/libvirt/images/guest1.img

• Test that the partition mapping worked. There should be new devices in the /dev/mapper/directory

# ls /dev/mapper/loop0p1loop0p2

The mappings for the image are named in the format loopXpY.

1 http://fedoraproject.org/wiki/EPEL

http://fedoraproject.org/wiki/EPEL

http://fedoraproject.org/wiki/EPEL


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4. Mount the loop device which to a directory. If required, create the directory. This example uses /mnt/guest1 for mounting the partition.

# mkdir /mnt/guest1# mount /dev/mapper/loop0p1 /mnt/guest1 -o loop,ro

5. The files are now available for reading in the /mnt/guest1 directory. Read or copy the files.

6. Unmount the device so the guest image can be reused by the guest. If the device is mounted theguest cannot access the image and therefore cannot start.

# umount /mnt/guest1

7. Disconnect the image file from the partition mappings.

# kpartx -d /var/lib/libvirt/images/guest1.img

The guest can now be restarted.

Accessing data from guest LVM volumesMany Linux guests use Logical Volume Management (LVM) volumes. Additional steps are required toread data on LVM volumes on virtual storage images.

1. Add the partition mappings for the guest1.img to the recognized devices in the /dev/mapper/directory.

# kpartx -a /var/lib/libvirt/images/guest1.img

2. In this example the LVM volumes are on a second partition. The volumes require a rescan withthe vgscan command to find the new volume groups.

# vgscanReading all physical volumes . This may take a while...Found volume group "VolGroup00" using metadata type lvm2

3. Activate the volume group on the partition (called VolGroup00 by default) with the vgchange -ay command.

# vgchange -ay VolGroup002 logical volumes in volume group VolGroup00 now active.

4. Use the lvs command to display information about the new volumes. The volume names (the LVcolumn) are required to mount the volumes.

# lvsLV VG Attr Lsize Origin Snap% Move Log Copy%LogVol00 VolGroup00 -wi-a- 5.06GLogVol01 VolGroup00 -wi-a- 800.00M

5. Mount /dev/VolGroup00/LogVol00 in the /mnt/guestboot/ directory.

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# mount /dev/VolGroup00/LogVol00 /mnt/guestboot

6. The files are now available for reading in the /mnt/guestboot directory. Read or copy the files.

7. Unmount the device so the guest image can be reused by the guest. If the device is mounted theguest cannot access the image and therefore cannot start.

# umount /mnt/guestboot

8. Disconnect the volume group VolGroup00

# vgchange -an VolGroup00

9. Disconnect the image file from the partition mappings.

# kpartx -d /var/lib/libvirt/images/guest1.img

The guest can now be restarted.

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Chapter 29.

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N_Port ID Virtualization (NPIV)N_Port ID Virtualization (NPIV) is a function available with some Fibre Channel devices. NPIV sharesa single physical N_Port as multiple N_Port IDs. NPIV provides similar functionality for Host BusAdaptors (HBAs) that SR-IOV provides for network interfaces. With NPIV, virtualized guests can beprovided with a virtual Fibre Channel initiator to Storage Area Networks (SANs).

N_Ports are addressed with a 24 bit N_Port ID, which is assigned by the Fibre Channel switch.

Why use NPIV• Without NPIV virtualized guests must share an HBA's WWN on the SAN. With NPIV, it is possible to

use LUN masking and zoning for virtualized guest.

• With NPIV migration with zones and LUN masking is possible.

• Physical HBAs are expensive and use an expansion slot. With NPIV, more guests can access SANresources and guest density can be increased.

Each N_Port has a unique identity (port WWN and node WWN) on the SAN and can be used forzoning and LUN masking. Soft zoning, which you can use to group ports together by port WWN, is thepreferred method of zoning.

29.1. Enabling NPIV on the switchEnabling the NPIV on a Fibre Channel port on a switch

admin> portcfgshow 0......NPIV capability ON......UsageportCfgNPIVPort <PortNumber> <Mode>Mode Meaning0 Disable the NPIV capability on the port1 Enable the NPIV capability on the port

Example:

admin> portCfgNPIVPort 0 1

29.1.1. Identifying HBAs in a Host SystemTo determine the types of HBAs in the system, enter the following command:

# ls /proc/scsiQLogic HBAs are listed as qla2xxx. Emulex HBAs are listed as lpfc.

QLogic Example

# ls /proc/scsi/qla2xxx

Emulex Example

# ls /proc/scsi/lpfc

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29.1.2. Verify NPIV is used on the HBAOutput the data from the kernel on the port nodes of the HBA.

Example 29.1. QLogic controller example

# cat /proc/scsi/qla2xxx/7FC Port Information for Virtual Ports:Virtual Port index = 1Virtual Port 1:VP State = <ACTIVE>, Vp Flags = 0x0scsiqla2port3=500601609020fd54:500601601020fd54:a00000:1000: 1;scsiqla2port4=500601609020fd54:500601681020fd54:a10000:1000: 1;Virtual Port 1 SCSI LUN Information:( 0:10): Total reqs 10, Pending reqs 0, flags 0x0, 2:0:1000,

Example 29.2. Emulex controller example

# cat /proc/scsi/lpfc/3SLI Rev: 3NPIV Supported: VPIs max 127 VPIs used 1RPIs max 512 RPIs used 13Vports list on this physical port:Vport DID 0x2f0901, vpi 1, state 0x20Portname: 48:19:00:0c:29:00:00:0d Nodename: 48:19:00:0c:29:00:00:0b

29.1.2.1. Create and destroy a virtual HBA with NPIVIssue an NPIV create call. Confirm that the host has started a new virtual HBA and that any storagezones are usable.

To create virtual HBAs using libvirt, you require a NPIV capable HBA and switch.

Confirm that you have those by manually creating a new HBA by printing the contents of the /sys/class/fc_host/hostN directory where class is the type of adaptor and fc_host is the hostnumber.

Note that the WWN used below are for demonstrative purposes only. Use WWN customized for yourSAN environment.

Add a new virtual HBA with the following command where'1111222233334444:5555666677778888' is WWPN:WWNN and host5 is the physical HBA whichthe virtual HBA is a client of.

# echo '1111222233334444:5555666677778888' > /sys/class/fc_host/host5/vport_create

If the creation is successful, a new HBA in the system with the next available host number.

Note

The virtual HBAs can be destroyed with the following command:

# echo '1111222233334444:5555666677778888' > /sys/class/fc_host/host5/vport_delete

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Adding the virtual HBA with virshThis procedure covers creating virtual HBA devices on a host with virsh. This procedure requires acompatible HBA device.

1. List available HBAsFind the node device name of the HBA with the virtual adapters. List of all the HBAs on the hostwith the following command:

# virsh nodedev-list -TODO-cap=scsi_hostpci_10df_fe00_0_scsi_hostpci_10df_fe00_0_scsi_host_0pci_10df_fe00_scsi_hostpci_10df_fe00_scsi_host_0pci_10df_fe00_scsi_host_0_scsi_hostpci_10df_fe00_scsi_host_0_scsi_host_0

2. Gather parent HBA device dataOutput the XML definition for each required HBA. This example uses the HBA,pci_10df_fe00_scsi_host.

# virsh nodedev-dumpxml pci_10df_fe00_scsi_host<device> <name>pci_10df_fe00_scsi_host</name> <parent>pci_10df_fe00</parent> <capability type='scsi_host'> <host>5</host> <capability type='fc_host'> <wwnn>20000000c9848140</wwnn> <wwpn>10000000c9848140</wwpn> </capability> <capability type='vport_ops' /> </capability></device>

HBAs capable of creating virtual HBAs have a capability type='vport_ops' in the XMLdefinition.

3. Create the XML definition for the virtual HBAWith information gathered in the previous step, create an XML definition for the virtual HBA. Thisexample uses a file named newHBA.xml.

<device> <parent>pci_10df_fe00_0_scsi_host</parent> <capability type='scsi_host'> <capability type='fc_host'> <wwpn>1111222233334444</wwpn> <wwnn>5555666677778888</wwnn> </capability> </capability></device>

The <parent> element is the name of the parent HBA listed by the virsh nodedev-listcommand. The <wwpn> and <wwnn> elements are the WWNN and WWPN for the virtual HBA.

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WWNN and WWPN validation

Libvirt does not validate the WWPN or WWNN values, invalid WWNs are rejected bythe kernel and libvirt reports the failure. The error reported by the kernel is similar to thefollowing:

# virsh nodedev-create badwwn.xmlerror: Failed to create node device from badwwn.xmlerror: Write of '1111222233334444:5555666677778888' to '/sys/class/fc_host/host6/vport_create' during vport create/delete failed: No such file or directory

4. Create the virtual HBACreate the virtual HBA with the virsh nodedev-create command using the file from theprevious step.

# virsh nodedev-create newHBA.xmlNode device pci_10df_fe00_0_scsi_host_0_scsi_host created from newHBA.xml

The new virtual HBA should be detected and available to the host. The create command outputgives you the node device name of the newly created device.

Destroying a virtual HBA with virsh

To destroy the device, use virsh nodedev-destroy:

# virsh nodedev-destroy pci_10df_fe00_0_scsi_host_0_scsi_hostDestroyed node device 'pci_10df_fe00_0_scsi_host_0_scsi_host'

Part VI. Virtualization reference guide

Virtualization commands,system tools, applications andadditional systems reference

These chapters provide detailed descriptions of virtualization commands, system tools, andapplications included in Red Hat Enterprise Linux 6. These chapters are designed for users requiringinformation on advanced functionality and other features.

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Managing guests with virshvirsh is a command line interface tool for managing guests and the hypervisor.

The virsh command-line tool is built on the libvirt management API and operates as analternative to the qemu-kvm command and the graphical virt-manager application. The virshcommand can be used in read-only mode by unprivileged users or, with root access, full administrationfunctionality. The virsh command is ideal for scripting virtualization administration.

virsh command quick referenceThe following tables provide a quick reference for all virsh command line options.

Table 30.1. Guest management commands

Command Description

help Prints basic help information.

list Lists all guests.

dumpxml Outputs the XML configuration file for the guest.

create Creates a guest from an XML configuration fileand starts the new guest.

start Starts an inactive guest.

destroy Forces a guest to stop.

define Outputs an XML configuration file for a guest.

domid Displays the guest's ID.

domuuid Displays the guest's UUID.

dominfo Displays guest information.

domname Displays the guest's name.

domstate Displays the state of a guest.

quit Quits the interactive terminal.

reboot Reboots a guest.

restore Restores a previously saved guest stored in afile.

resume Resumes a paused guest.

save Save the present state of a guest to a file.

shutdown Gracefully shuts down a guest.

suspend Pauses a guest.

undefine Deletes all files associated with a guest.

migrate Migrates a guest to another host.

The following virsh command options manage guest and hypervisor resources:

Table 30.2. Resource management options

Command Description

setmem Sets the allocated memory for a guest.

setmaxmem Sets maximum memory limit for the hypervisor.

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Command Description

setvcpus Changes number of virtual CPUs assigned to aguest.

vcpuinfo Displays virtual CPU information about a guest.

vcpupin Controls the virtual CPU affinity of a guest.

domblkstat Displays block device statistics for a runningguest.

domifstat Displays network interface statistics for a runningguest.

attach-device Attach a device to a guest, using a devicedefinition in an XML file.

attach-disk Attaches a new disk device to a guest.

attach-interface Attaches a new network interface to a guest.

detach-device Detach a device from a guest, takes the samekind of XML descriptions as command attach-device.

detach-disk Detach a disk device from a guest.

detach-interface Detach a network interface from a guest.

The virsh commands for managing and creating storage pools and volumes.

For more information on using storage pools with virsh, refer to http://libvirt.org/formatstorage.html

Table 30.3. Storage Pool options

Command Description

find-storage-pool-sources Returns the XML definition for all storage poolsof a given type that could be found.

find-storage-pool-sources port Returns data on all storage pools of a given typethat could be found as XML. If the host and portare provided, this command can be run remotely.

pool-autostart Sets the storage pool to start at boot time.

pool-build The pool-build command builds a definedpool. This command can format disks and createpartitions.

pool-create pool-create creates and starts a storage poolfrom the provided XML storage pool definitionfile.

pool-create-as name Creates and starts a storage pool from theprovided parameters. If the --print-xmlparameter is specified, the command printsthe XML definition for the storage pool withoutcreating the storage pool.

pool-define Creates a storage bool from an XML definitionfile but does not start the new storage pool.

pool-define-as name Creates but does not start, a storage pool fromthe provided parameters. If the --print-xmlparameter is specified, the command prints

http://libvirt.org/formatstorage.html

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Command Descriptionthe XML definition for the storage pool withoutcreating the storage pool.

pool-destroy Permanently destroys a storage pool inlibvirt. The raw data contained in the storagepool is not changed and can be recovered withthe pool-create command.

pool-delete Destroys the storage resources used bya storage pool. This operation cannot berecovered. The storage pool still exists after thiscommand but all data is deleted.

pool-dumpxml Prints the XML definition for a storage pool.

pool-edit Opens the XML definition file for a storage poolin the users default text editor.

pool-info Returns information about a storage pool.

pool-list Lists storage pools known to libvirt. By default,pool-list lists pools in use by active guests.The --inactive parameter lists inactive poolsand the --all parameter lists all pools.

pool-undefine Deletes the definition for an inactive storagepool.

pool-uuid Returns the UUID of the named pool.

pool-name Prints a storage pool's name when provided theUUID of a storage pool.

pool-refresh Refreshes the list of volumes contained in astorage pool.

pool-start Starts a storage pool that is defined but inactive.

This table contains miscellaneous virsh commands:

Table 30.4. Miscellaneous options

Command Description

version Displays the version of virsh

nodeinfo Outputs information about the hypervisor

Connecting to the hypervisorConnect to a hypervisor session with virsh:

# virsh connect {name}

Where {name} is the machine name (hostname) or URL of the hypervisor. To initiate a read-onlyconnection, append the above command with --readonly.

Creating a virtual machine XML dump (configuration file)Output a guest's XML configuration file with virsh:

# virsh dumpxml {guest-id, guestname or uuid}


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This command outputs the guest's XML configuration file to standard out (stdout). You can save thedata by piping the output to a file. An example of piping the output to a file called guest.xml:

# virsh dumpxml GuestID > guest.xml

This file guest.xml can recreate the guest (refer to Editing a guest's configuration file. You can editthis XML configuration file to configure additional devices or to deploy additional guests. Refer toSection 33.1, “Using XML configuration files with virsh” for more information on modifying files createdwith virsh dumpxml.

An example of virsh dumpxml output:

# virsh dumpxml r5b2-mySQL01<domain type='kvm' id='13'> <name>r5b2-mySQL01</name> <uuid>4a4c59a7ee3fc78196e4288f2862f011</uuid> <bootloader>/usr/bin/pygrub</bootloader> <os> <type>linux</type> <kernel>/var/lib/libvirt/vmlinuz.2dgnU_</kernel> <initrd>/var/lib/libvirt/initrd.UQafMw</initrd> <cmdline>ro root=/dev/VolGroup00/LogVol00 rhgb quiet</cmdline> </os> <memory>512000</memory> <vcpu>1</vcpu> <on_poweroff>destroy</on_poweroff> <on_reboot>restart</on_reboot> <on_crash>restart</on_crash> <devices> <interface type='bridge'> <source bridge='br0'/> <mac address='00:16:3e:49:1d:11'/> <script path='bridge'/> </interface> <graphics type='vnc' port='5900'/> <console tty='/dev/pts/4'/> </devices></domain>

Creating a guest from a configuration fileGuests can be created from XML configuration files. You can copy existing XML from previouslycreated guests or use the dumpxml option (refer to Creating a virtual machine XML dump(configuration file)). To create a guest with virsh from an XML file:

# virsh create configuration_file.xml

Editing a guest's configuration fileInstead of using the dumpxml option (refer to Creating a virtual machine XML dump (configurationfile)) guests can be edited either while they run or while they are offline. The virsh edit commandprovides this functionality. For example, to edit the guest named softwaretesting:

# virsh edit softwaretesting

This opens a text editor. The default text editor is the $EDITOR shell parameter (set to vi by default).

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Suspending a guestSuspend a guest with virsh:

# virsh suspend {domain-id, domain-name or domain-uuid}

When a guest is in a suspended state, it consumes system RAM but not processor resources. Diskand network I/O does not occur while the guest is suspended. This operation is immediate and theguest can be restarted with the resume (Resuming a guest) option.

Resuming a guestRestore a suspended guest with virsh using the resume option:

# virsh resume {domain-id, domain-name or domain-uuid}

This operation is immediate and the guest parameters are preserved for suspend and resumeoperations.

Save a guestSave the current state of a guest to a file using the virsh command:

# virsh save {domain-name, domain-id or domain-uuid} filename

This stops the guest you specify and saves the data to a file, which may take some time given theamount of memory in use by your guest. You can restore the state of the guest with the restore(Restore a guest) option. Save is similar to pause, instead of just pausing a guest the present state ofthe guest is saved.

Restore a guestRestore a guest previously saved with the virsh save command (Save a guest) using virsh:

# virsh restore filename

This restarts the saved guest, which may take some time. The guest's name and UUID are preservedbut are allocated for a new id.

Shut down a guestShut down a guest using the virsh command:

# virsh shutdown {domain-id, domain-name or domain-uuid}

You can control the behavior of the rebooting guest by modifying the on_shutdown parameter in theguest's configuration file.

Rebooting a guestReboot a guest using virsh command:

#virsh reboot {domain-id, domain-name or domain-uuid}


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You can control the behavior of the rebooting guest by modifying the on_reboot element in theguest's configuration file.

Forcing a guest to stopForce a guest to stop with the virsh command:

# virsh destroy {domain-id, domain-name or domain-uuid}

This command does an immediate ungraceful shutdown and stops the specified guest. Usingvirsh destroy can corrupt guest file systems . Use the destroy option only when the guest isunresponsive.

Getting the domain ID of a guestTo get the domain ID of a guest:

# virsh domid {domain-name or domain-uuid}

Getting the domain name of a guestTo get the domain name of a guest:

# virsh domname {domain-id or domain-uuid}

Getting the UUID of a guestTo get the Universally Unique Identifier (UUID) for a guest:

# virsh domuuid {domain-id or domain-name}

An example of virsh domuuid output:

# virsh domuuid r5b2-mySQL014a4c59a7-ee3f-c781-96e4-288f2862f011

Displaying guest InformationUsing virsh with the guest's domain ID, domain name or UUID you can display information on thespecified guest:

# virsh dominfo {domain-id, domain-name or domain-uuid}

This is an example of virsh dominfo output:

# virsh dominfo r5b2-mySQL01id: 13name: r5b2-mysql01uuid: 4a4c59a7-ee3f-c781-96e4-288f2862f011os type: linuxstate: blockedcpu(s): 1cpu time: 11.0smax memory: 512000 kb

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used memory: 512000 kb

Displaying host informationTo display information about the host:

# virsh nodeinfo

An example of virsh nodeinfo output:

# virsh nodeinfoCPU model x86_64CPU (s) 8CPU frequency 2895 MhzCPU socket(s) 2 Core(s) per socket 2Threads per core: 2Numa cell(s) 1Memory size: 1046528 kb

This displays the node information and the machines that support the virtualization process.

Editing a storage pool definitionThe virsh pool-edit command takes the name or UUID for a storage pool and opens the XMLdefinition file for a storage pool in the users default text editor.

The virsh pool-edit command is equivalent to running the following commands:

# virsh pool-dumpxml pool > pool.xml# vim pool.xml# virsh pool-define pool.xml

Note

The default editor is defined by the $VISUAL or $EDITOR environment variables, and default isvi.

Displaying the guestsTo display the guest list and their current states with virsh:

# virsh list

Other options available include:

the --inactive option to list inactive guests (that is, guests that have been defined but are notcurrently active), and

the --all option lists all guests. For example:

# virsh list --all Id Name State---------------------------------- 0 Domain-0 running 1 Domain202 paused


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2 Domain010 inactive 3 Domain9600 crashed

The output from virsh list is categorized as one of the six states (listed below).

• The running state refers to guests which are currently active on a CPU.

• Guests listed as blocked are blocked, and are not running or runnable. This is caused by a guestwaiting on I/O (a traditional wait state) or guests in a sleep mode.

• The paused state lists domains that are paused. This occurs if an administrator uses the pausebutton in virt-manager, xm pause or virsh suspend. When a guest is paused it consumesmemory and other resources but it is ineligible for scheduling and CPU resources from thehypervisor.

• The shutdown state is for guests in the process of shutting down. The guest is sent a shutdownsignal and should be in the process of stopping its operations gracefully. This may not work with allguest operating systems; some operating systems do not respond to these signals.

• Domains in the dying state are in is in process of dying, which is a state where the domain has notcompletely shut-down or crashed.

• crashed guests have failed while running and are no longer running. This state can only occur ifthe guest has been configured not to restart on crash.

Displaying virtual CPU informationTo display virtual CPU information from a guest with virsh:

# virsh vcpuinfo {domain-id, domain-name or domain-uuid}

An example of virsh vcpuinfo output:

# virsh vcpuinfo r5b2-mySQL01VCPU: 0CPU: 0State: blockedCPU time: 0.0sCPU Affinity: yy

Configuring virtual CPU affinityTo configure the affinity of virtual CPUs with physical CPUs:

# virsh vcpupin domain-id vcpu cpulist

The domain-id parameter is the guest's ID number or name.

The vcpu parameter denotes the number of virtualized CPUs allocated to the guest.The vcpuparameter must be provided.

The cpulist parameter is a list of physical CPU identifier numbers separated by commas. Thecpulist parameter determines which physical CPUs the VCPUs can run on.

Configuring virtual CPU countTo modify the number of CPUs assigned to a guest with virsh:

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# virsh setvcpus {domain-name, domain-id or domain-uuid} count

The new count value cannot exceed the count above the amount specified when the guest wascreated.

Configuring memory allocationTo modify a guest's memory allocation with virsh :

# virsh setmem {domain-id or domain-name} count

You must specify the count in kilobytes. The new count value cannot exceed the amount you specifiedwhen you created the guest. Values lower than 64 MB are unlikely to work with most guest operatingsystems. A higher maximum memory value does not affect an active guests. If the new value is lowerthe available memory will shrink and the guest may crash.

Displaying guest block device informationUse virsh domblkstat to display block device statistics for a running guest.

# virsh domblkstat GuestName block-device

Displaying guest network device informationUse virsh domifstat to display network interface statistics for a running guest.

# virsh domifstat GuestName interface-device

Migrating guests with virshA guest can be migrated to another host with virsh. Migrate domain to another host. Add --live forlive migration. The migrate command accepts parameters in the following format:

# virsh migrate --live GuestName DestinationURL

The --live parameter is optional. Add the --live parameter for live migrations.

The GuestName parameter represents the name of the guest which you want to migrate.

The DestinationURL parameter is the URL or hostname of the destination system. The destinationsystem requires:

• Red Hat Enterprise Linux 5.4 (ASYNC update 4) or newer,

• the same hypervisor version, and

• the libvirt service must be started.

Once the command is entered you will be prompted for the root password of the destination system.

Managing virtual networksThis section covers managing virtual networks with the virsh command. To list virtual networks:


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# virsh net-list

This command generates output similar to:

# virsh net-listName State Autostart-----------------------------------------default active yes vnet1 active yes vnet2 active yes

To view network information for a specific virtual network:

# virsh net-dumpxml NetworkName

This displays information about a specified virtual network in XML format:

# virsh net-dumpxml vnet1<network> <name>vnet1</name> <uuid>98361b46-1581-acb7-1643-85a412626e70</uuid> <forward dev='eth0'/> <bridge name='vnet0' stp='on' forwardDelay='0' /> <ip address='192.168.100.1' netmask='255.255.255.0'> <dhcp> <range start='192.168.100.128' end='192.168.100.254' /> </dhcp> </ip></network>

Other virsh commands used in managing virtual networks are:

• virsh net-autostart network-name — Autostart a network specified as network-name.

• virsh net-create XMLfile — generates and starts a new network using an existing XML file.

• virsh net-define XMLfile — generates a new network device from an existing XML filewithout starting it.

• virsh net-destroy network-name — destroy a network specified as network-name.

• virsh net-name networkUUID — convert a specified networkUUID to a network name.

• virsh net-uuid network-name — convert a specified network-name to a network UUID.

• virsh net-start nameOfInactiveNetwork — starts an inactive network.

• virsh net-undefine nameOfInactiveNetwork — removes the definition of an inactivenetwork.

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Managing guests with the VirtualMachine Manager (virt-manager)This section describes the Virtual Machine Manager (virt-manager) windows, dialog boxes, andvarious GUI controls.

virt-manager provides a graphical view of hypervisors and guest on your system and on remotemachines. You can use virt-manager to define virtualized guests. virt-manager can performvirtualization management tasks, including:

• assigning memory,

• assigning virtual CPUs,

• monitoring operational performance,

• saving and restoring, pausing and resuming, and shutting down and starting virtualized guests,

• links to the textual and graphical consoles, and

• live and offline migrations.

31.1. Starting virt-managerTo start virt-manager session open the Applications menu, then the System Tools menu andselect Virtual Machine Manager (virt-manager).

The virt-manager main window appears.

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Figure 31.1. Starting virt-manager

Alternatively, virt-manager can be started remotely using ssh as demonstrated in the followingcommand:

ssh -X host's address[remotehost]# virt-manager

Using ssh to manage virtual machines and hosts is discussed further in Section 19.1, “Remotemanagement with SSH”.

31.2. The Virtual Machine Manager main windowThis main window displays all the running guests and resources used by guests. Select a virtualizedguest by double clicking the guest's name.

The virtual hardware details window

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Figure 31.2. Virtual Machine Manager main window

31.3. The virtual hardware details windowThe virtual hardware details window displays information about the virtual hardware configured for thevirtualized guest. Virtual hardware resources can be added, removed and modified in this window. Toaccess the virtual hardware details window, click on the icon in the toolbar.


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Figure 31.3. The virtual hardware details icon

Clicking the icon displays the virtual hardware details window.

Virtual Machine graphical console

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Figure 31.4. The virtual hardware details window

31.4. Virtual Machine graphical consoleThis window displays a virtualized guest's graphical console. Virtualized guests use differenttechniques to export their local virtual framebuffers, but both technologies use VNC to make themavailable to the Virtual Machine Manager's console window. If your virtual machine is set to requireauthentication, the Virtual Machine graphical console prompts you for a password before the displayappears.


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Figure 31.5. Graphical console window

A note on security and VNC

VNC is considered insecure by many security experts, however, several changes have beenmade to enable the secure usage of VNC for virtualization on Red Hat enterprise Linux. Theguest machines only listen to the local host's loopback address (127.0.0.1). This ensures onlythose with shell privileges on the host can access virt-manager and the virtual machine throughVNC.

Remote administration can be performed following the instructions in Chapter 19, Remotemanagement of virtualized guests. TLS can provide enterprise level security for managing guestand host systems.

Your local desktop can intercept key combinations (for example, Ctrl+Alt+F11) to prevent them frombeing sent to the guest machine. You can use virt-managersticky key' capability to send thesesequences. You must press any modifier key (Ctrl or Alt) 3 times and the key you specify gets treatedas active until the next non-modifier key is pressed. Then you can send Ctrl-Alt-F11 to the guest byentering the key sequence 'Ctrl Ctrl Ctrl Alt+F1'.

SPICE is an alternative to VNC available for Red Hat Enterprise Linux.

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31.5. Adding a remote connectionThis procedure covers how to set up a connection to a remote system using virt-manager.

1. To create a new connection open the File menu and select the Add Connection... menu item.

2. The Add Connection wizard appears. Select the hypervisor. For Red Hat Enterprise Linux 6systems select QEMU/KVM. Select Local for the local system or one of the remote connectionoptions and click Connect. This example uses Remote tunnel over SSH which works on defaultinstallations. For more information on configuring remote connections refer to Chapter 19, Remotemanagement of virtualized guests

Figure 31.6. Add Connection

3. Enter the root password for the selected host when prompted.

A remote host is now connected and appears in the main virt-manager window.


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Figure 31.7. Remote host in the main virt-manager window

31.6. Displaying guest detailsYou can use the Virtual Machine Monitor to view activity information for any virtual machines on yoursystem.

To view a virtual system's details:

Displaying guest details

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1. In the Virtual Machine Manager main window, highlight the virtual machine that you want to view.

Figure 31.8. Selecting a virtual machine to display


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2. From the Virtual Machine Manager Edit menu, select Virtual Machine Details.

Figure 31.9. Displaying the virtual machine details

On the Virtual Machine window, select Overview from the navigation pane on the left hand side.

The Overview view shows a summary of configuration details for the virtualized guest.


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Figure 31.10. Displaying guest details overview

3. Select Performance from the navigation pane on the left hand side.

The Performance view shows a summary of guest performance, including CPU and Memoryusage.


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Figure 31.11. Displaying guest performance details


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4. Select Processor from the navigation pane on the left hand side. The Processor view allows youto view or change the current processor allocation.

Figure 31.12. Processor allocation panel


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5. Select Memory from the navigation pane on the left hand side. The Memory view allows you toview or change the current memory allocation.

Figure 31.13. Displaying memory allocation

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6. Each virtual disk attached to the virtual machine is displayed in the navigation pane. Click on avirtual disk to modify or remove it.

Figure 31.14. Displaying disk configuration

7. Each virtual network interface attached to the virtual machine is displayed in the nagivation pane.Click on a virtual network interface to modify or remove it.

Figure 31.15. Displaying network configuration

31.7. Performance monitoringPerformance monitoring preferences can be modified with virt-manager's preferences window.

To configure Performance monitoring:


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1. From the Edit menu, select Preferences.

Figure 31.16. Modifying guest preferences

The Preferences window appears.

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2. From the Stats tab specify the time in seconds or stats polling options.

Figure 31.17. Configuring performance monitoring

31.8. Displaying CPU usageTo view the CPU usage for all virtual machines on your system:


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1. From the View menu, select Graph, then the CPU Usage check box.

Figure 31.18. Selecting CPU usage

2. The Virtual Machine Manager shows a graph of CPU usage for all virtual machines on yoursystem.

Figure 31.19. Displaying CPU usage

31.9. Displaying Disk I/OTo view the disk I/O for all virtual machines on your system:

Displaying Network I/O

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1. From the View menu, select Graph, then the Disk I/O check box.

Figure 31.20. Selecting Disk I/O

2. The Virtual Machine Manager shows a graph of Disk I/O for all virtual machines on your system.

Figure 31.21. Displaying Disk I/O

31.10. Displaying Network I/OTo view the network I/O for all virtual machines on your system:


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1. From the View menu, select Graph, then the Network I/O check box.

Figure 31.22. Selecting Network I/O

2. The Virtual Machine Manager shows a graph of Network I/O for all virtual machines on yoursystem.

Figure 31.23. Displaying Network I/O

31.11. Managing a virtual networkTo configure a virtual network on your system:

Managing a virtual network

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1. From the Edit menu, select Host Details.

Figure 31.24. Selecting a host's details


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2. This will open the Host Details menu. Click the Virtual Networks tab.

Figure 31.25. Virtual network configuration

3. All available virtual networks are listed on the left-hand box of the menu. You can edit theconfiguration of a virtual network by selecting it from this box and editing as you see fit.

31.12. Creating a virtual networkTo create a virtual network on your system:

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1. Open the Host Details menu (refer to Section 31.11, “Managing a virtual network”) and click theAdd Network button, identified by a plus sign (+) icon.

Figure 31.26. Virtual network configuration

This will open the Create a new virtual network window. Click Forward to continue.


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Figure 31.27. Creating a new virtual network


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2. Enter an appropriate name for your virtual network and click Forward.

Figure 31.28. Naming your virtual network


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3. Enter an IPv4 address space for your virtual network and click Forward.

Figure 31.29. Choosing an IPv4 address space


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4. Define the DHCP range for your virtual network by specifying a Start and End range of IPaddresses. Click Forward to continue.

Figure 31.30. Selecting the DHCP range


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5. Select how the virtual network should connect to the physical network.

Figure 31.31. Connecting to physical network

If you select Forwarding to physical network, choose whether the Destination should be Anyphysical device or a specific physical device. Also select whether the Mode should be NAT orRouted.



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6. You are now ready to create the network. Check the configuration of your network and clickFinish.

Figure 31.32. Ready to create network


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7. The new virtual network is now available in the Virtual Network tab of the Host Details window.

Figure 31.33. New virtual network is now available

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libvirt configuration referenceThis chapter provides is a references for various parameters of libvirt XML configuration files

Table 32.1. libvirt configuration files

Item Description

pae Specifies the physical address extensionconfiguration data.

apic Specifies the advanced programmable interruptcontroller configuration data.

memory Specifies the memory size in megabytes.

vcpus Specifies the numbers of virtual CPUs.

console Specifies the port numbers to export the domainconsoles to.

nic Specifies the number of virtual networkinterfaces.

vif Lists the randomly-assigned MAC addresses andbridges assigned to use for the domain's networkaddresses.

disk Lists the block devices to export to the domainand exports physical devices to domain with readonly access.

dhcp Enables networking using DHCP.

netmask Specifies the configured IP netmasks.

gateway Specifies the configured IP gateways.

acpi Specifies the advanced configuration powerinterface configuration data.

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Chapter 33.

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Creating custom libvirt scriptsThis section provides some information which may be useful to programmers and systemadministrators intending to write custom scripts to make their lives easier by using libvirt.

Chapter 24, Miscellaneous administration tasks is recommended reading for programmers thinking ofwriting new applications which use libvirt.

33.1. Using XML configuration files with virshvirsh can handle XML configuration files. You may want to use this to your advantage for scriptinglarge deployments with special options. You can add devices defined in an XML file to a runningvirtualized guest. For example, to add a ISO file as hdc to a running guest create an XML file:

# cat satelliteiso.xml<disk type="file" device="disk"> <driver name="file"/> <source file="/var/lib/libvirt/images/rhn-satellite-5.0.1-11-redhat-linux-as-i386-4-embedded-oracle.iso"/> <target dev="hdc"/> <readonly/></disk>

Run virsh attach-device to attach the ISO as hdc to a guest called "satellite" :

# virsh attach-device satellite satelliteiso.xml

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Part VII. Troubleshooting

Introduction to troubleshootingand problem solving

The following chapters provide information to assist you in troubleshooting issues you may encounterusing virtualization.

Important note on virtualization issues

Your particular problem may not appear in this book due to ongoing development which createsand fixes bugs. For the most up to date list of known bugs, issues and bug fixes read the RedHat Enterprise Linux 6 Release Notes for your version and hardware architecture. The ReleaseNotes can be found in the documentation section of the Red Hat website, www.redhat.com/docs/manuals/enterprise/1.

If all else fails...

Contact Red Hat Global Support Services (https://www.redhat.com/apps/support/). Our staff canassist you in resolving your issues.




https://www.redhat.com/apps/support/


Chapter 34.

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TroubleshootingThis chapter covers common problems and solutions for Red Hat Enterprise Linux 6 virtualizationissues.

This chapter is to give you, the reader, a background to identify where problems with virtualizationtechnologies are. Troubleshooting takes practice and experience which are difficult to learn from abook. It is recommended that you experiment and test virtualization on Red Hat Enterprise Linux 6 todevelop your troubleshooting skills.

If you cannot find the answer in this document there may be an answer online from the virtualizationcommunity. Refer to Section A.1, “Online resources” for a list of Linux virtualization websites.

34.1. Debugging and troubleshooting toolsThis section summarizes the System Administrator applications, the networking utilities, anddebugging tools. You can employ these standard System administration tools and logs to assist withtroubleshooting:

• kvm_stat

• kvmtrace

• vmstat

• iostat

• lsof

• systemtap

• crash

• sysrq

• sysrq t

• sysrq w

These networking tools can assist with troubleshooting virtualization networking problems:

• ifconfig

• tcpdump

The tcpdump command 'sniffs' network packets. tcpdump is useful for finding networkabnormalities and problems with network authentication. There is a graphical version of tcpdumpnamed wireshark.

• brctl

brctl is a networking tool that inspects and configures the Ethernet bridge configuration in theVirtualization linux kernel. You must have root access before performing these example commands:

# brctl show bridge-name bridge-id STP enabled interfaces -----------------------------------------------------------------------------virtbr0 8000.feffffff yes eth0

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# brctl showmacs virtbr0 port-no mac-addr local? aging timer1 fe:ff:ff:ff:ff: yes 0.002 fe:ff:ff:fe:ff: yes 0.00# brctl showstp virtbr0virtbr0 bridge-id 8000.fefffffffffdesignated-root 8000.fefffffffffroot-port 0 path-cost 0max-age 20.00 bridge-max-age 20.00hello-time 2.00 bridge-hello-time 2.00forward-delay 0.00 bridge-forward-delay 0.00aging-time 300.01hello-timer 1.43 tcn-timer 0.00topology-change-timer 0.00 gc-timer 0.02

Listed below are some other useful commands for troubleshooting virtualization.

• strace is a command which traces system calls and events received and used by another process.

• vncviewer: connect to a VNC server running on your server or a virtual machine. Install vncviwerusing the yum install vnc command.

• vncserver: start a remote desktop on your server. Gives you the ability to run graphical userinterfaces such as virt-manager via a remote session. Install vncserver using the yum installvnc-server command.

34.2. kvm_statThe kvm_stat command is a python script which retrieves runtime statistics from the kvm kernelmodule. The kvm_stat command can be used to diagnose guest behavior visible to kvm. Inparticular, performance related issues with guests. Currently, the reported statistics are for the entiresystem; the behavior of all running guests is reported.

The kvm_stat command requires that the kvm kernel module is loaded and debugfs is mounted.If either of these features are not enabled, the command will output the required steps to enabledebugfs or the kvm module. For example:

# kvm_statPlease mount debugfs ('mount -t debugfs debugfs /sys/kernel/debug')and ensure the kvm modules are loaded

Mount debugfs if required:

# mount -t debugfs debugfs /sys/kernel/debug

kvm_stat outputThe kvm_stat command outputs statistics for all virtualized guests and the host. The output isupdated until the command is terminated (using Ctrl+c or the q key).

# kvm_stat

kvm statistics

efer_reload 94 0exits 4003074 31272fpu_reload 1313881 10796

kvm_stat

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halt_exits 14050 259halt_wakeup 4496 203host_state_reload 1638354 24893hypercalls 0 0insn_emulation 1093850 1909insn_emulation_fail 0 0invlpg 75569 0io_exits 1596984 24509irq_exits 21013 363irq_injections 48039 1222irq_window 24656 870largepages 0 0mmio_exits 11873 0mmu_cache_miss 42565 8mmu_flooded 14752 0mmu_pde_zapped 58730 0mmu_pte_updated 6 0mmu_pte_write 138795 0mmu_recycled 0 0mmu_shadow_zapped 40358 0mmu_unsync 793 0nmi_injections 0 0nmi_window 0 0pf_fixed 697731 3150pf_guest 279349 0remote_tlb_flush 5 0request_irq 0 0signal_exits 1 0tlb_flush 200190 0

Explanation of variables:efer_reload

The number of Extended Feature Enable Register (EFER) reloads.

exitsThe count of all VMEXIT calls.

fpu_reloadThe number of times a VMENTRY reloaded the FPU state. The fpu_reload is incremented whena guest is using the Floating Point Unit (FPU).

halt_exitsNumber of guest exits due to halt calls. This type of exit is usually seen when a guest is idle.

halt_wakeupNumber of wakeups from a halt.

host_state_reloadCount of full reloads of the host state (currently tallies MSR setup and guest MSR reads).

hypercallsNumber of guest hypervisor service calls.

insn_emulationNumber of guest instructions emulated by the host.

insn_emulation_failNumber of failed insn_emulation attempts.

io_exitsNumber of guest exits from I/O port accesses.


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irq_exitsNumber of guest exits due to external interrupts.

irq_injectionsNumber of interrupts sent to guests.

irq_windowNumber of guest exits from an outstanding interrupt window.

largepagesNumber of large pages currently in use.

mmio_exitsNumber of guest exits due to memory mapped I/O (MMIO) accesses.

mmu_cache_missNumber of KVM MMU shadow pages created.

mmu_floodedDetection count of excessive write operations to an MMU page. This counts detected writeoperations not of individual write operations.

mmu_pde_zappedNumber of page directory entry (PDE) destruction operations.

mmu_pte_updatedNumber of page table entry (PTE) destruction operations.

mmu_pte_writeNumber of guest page table entry (PTE) write operations.

mmu_recycledNumber of shadow pages that can be reclaimed.

mmu_shadow_zappedNumber of invalidated shadow pages.

mmu_unsyncNumber of non-synchronized pages which are not yet unlinked.

nmi_injectionsNumber of Non-maskable Interrupt (NMI) injections to the guest.

nmi_windowNumber of guest exits from (outstanding) Non-maskable Interrupt (NMI) windows.

pf_fixedNumber of fixed (non-paging) page table entry (PTE) maps.

pf_guestNumber of page faults injected into guests.

remote_tlb_flushNumber of remote (sibling CPU) Translation Lookaside Buffer (TLB) flush requests.

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request_irqNumber of guest interrupt window request exits.

signal_exitsNumber of guest exits due to pending signals from the host.

tlb_flushNumber of tlb_flush operations performed by the hypervisor.

Note

The output information from the kvm_stat command is exported by the KVM hypervisor aspseudo files located in the /sys/kernel/debug/kvm/ directory.

34.3. Log filesKVM uses various log files. All the log files are standard ASCII files, and accessible with a text editor.

• The default directory for all file-based images is the /var/lib/libvirt/images directory.

• qemu-kvm.[PID].log is the log file created by the qemu-kvm process for each fully virtualizedguest. When using this log file, you must retrieve the given qemu-kvm process PID, by using the pscommand to examine process arguments to isolate the qemu-kvm process on the virtual machine.Note that you must replace the [PID] symbol with the actual PID qemu-kvm process.

If you encounter any errors with the Virtual Machine Manager, you can review the generated data inthe virt-manager.log file that resides in the /.virt-manager directory. Note that every timeyou start the Virtual Machine Manager, it overwrites the existing log file contents. Make sure to backupthe virt-manager.log file, before you restart the Virtual Machine manager after a system error.

34.4. Troubleshooting with serial consolesLinux kernels can output information to serial ports. This is useful for debugging kernel panics andhardware issues with video devices or headless servers. The subsections in this section cover settingup serial console output for machines running Red Hat Enterprise Linux 6 virtualization kernels andtheir virtualized guests.

This section covers how to enable serial console output for fully virtualized guests.

Fully virtualized guest serial console output can be viewed with the virsh console command.

Be aware fully virtualized guest serial consoles have some limitations. Present limitations include:

• output data may be dropped or scrambled.

The serial port is called ttyS0 on Linux or COM1 on Windows.

You must configure the virtualized operating system to output information to the virtual serial port.

To output kernel information from a fully virtualized Linux guest into the domain modify the /boot/grub/grub.conf file by inserting the line console=tty0 console=ttyS0,115200.

title Red Hat Enterprise Linux Server (2.6.32-36.x86-64) root (hd0,0) kernel /vmlinuz-2.6.32-36.x86-64 ro root=/dev/volgroup00/logvol00 console=tty0 console=ttyS0,115200


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initrd /initrd-2.6.32-36.x86-64.img

Reboot the guest.

On the host, access the serial console with the following command:

# virsh console

You can also use virt-manager to display the virtual text console. In the guest console window,select Serial Console from the View menu.

34.5. Virtualization log files• /var/log/libvirt/qemu/GuestName.log

If you encounter any errors with the Virtual Machine Manager, you can review the generated data inthe virt-manager.log file that resides in the /.virt-manager directory. Note that every timeyou start the Virtual Machine Manager, it overwrites the existing log file contents. Make sure to backupthe virt-manager.log file, before you restart the Virtual Machine manager after a system error.

34.6. Loop device errorsIf file-based guest images are used you may have to increase the number of configured loop devices.The default configuration allows up to eight active loop devices. If more than eight file-based guestsor loop devices are needed the number of loop devices configured can be adjusted in /etc/modprobe.conf. Edit /etc/modprobe.conf and add the following line to it:

options loop max_loop=64

This example uses 64 but you can specify another number to set the maximum loop value. You mayalso have to implement loop device backed guests on your system. To use a loop device backedguests for a full virtualized system, use the phy: device or file: file commands.

34.7. Enabling Intel VT and AMD-V virtualization hardwareextensions in BIOSThis section describes how to identify hardware virtualization extensions and enable them in yourBIOS if they are disabled.

The Intel VT extensions can be disabled in the BIOS. Certain laptop vendors have disabled the IntelVT extensions by default in their CPUs.

The virtualization extensions cannot be disabled in the BIOS for AMD-V.

The virtualization extensions are sometimes disabled in BIOS, usually by laptop manufacturers. Referto the following section for instructions on enabling disabled virtualization extensions.

Verify the virtualization extensions are enabled in BIOS. The BIOS settings for Intel® VT or AMD-V are usually in the Chipset or Processor menus. The menu names may vary from this guide, thevirtualization extension settings may be found in Security Settings or other non standard menunames.

Procedure 34.1. Enabling virtualization extensions in BIOS1. Reboot the computer and open the system's BIOS menu. This can usually be done by pressing

the delete key, the F1 key or Alt and F4 keys depending on the system.

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2. Enabling the virtualization extensions in BIOS

Note: BIOS steps

Many of the steps below may vary depending on your motherboard, processor type, chipsetand OEM. Refer to your system's accompanying documentation for the correct informationon configuring your system.

a. Open the Processor submenu The processor settings menu may be hidden in the Chipset,Advanced CPU Configuration or Northbridge.

b. Enable Intel Virtualization Technology (also known as Intel VT). AMD-V extensions cannotbe disabled in the BIOS and should already be enabled. The virtualization extensions may belabeled Virtualization Extensions, Vanderpool or various other names depending on theOEM and system BIOS.

c. Enable Intel VTd or AMD IOMMU, if the options are available. Intel VTd and AMD IOMMUare used for PCI passthrough.

d. Select Save & Exit.

3. Reboot the machine.

4. When the machine has booted, run cat /proc/cpuinfo | grep vmx svm. If the commandoutputs, the virtualization extensions are now enabled. If there is no output your system may nothave the virtualization extensions or the correct BIOS setting enabled.

34.8. KVM networking performanceBy default, KVM virtual machines are assigned a virtual Realtek 8139 (rtl8139) NIC (network interfacecontroller).

The rtl8139 virtualized NIC works fine in most environments. However, this device can suffer fromperformance degradation problems on some networks, for example, a 10 Gigabit Ethernet network.

To improve performance switch to the para-virtualized network driver.

Note

Note that the virtualized Intel PRO/1000 (e1000) driver is also supported as an emulated driverchoice. To use the e1000 driver, replace virtio in the procedure below with e1000. For thebest performance it is recommended to use the virtio driver.

Procedure 34.2. Switching to the virtio driver1. Shutdown the guest operating system.

2. Edit the guest's configuration file with the virsh command (where GUEST is the guest's name):

# virsh edit GUEST

The virsh edit command uses the $EDITOR shell variable to determine which editor to use.


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3. Find the network interface section of the configuration. This section resembles the snippet below:

<interface type='network'> [output truncated] <model type='rtl8139' /></interface>

4. Change the type attribute of the model element from 'rtl8139' to 'virtio'. This will changethe driver from the rtl8139 driver to the e1000 driver.

<interface type='network'> [output truncated] <model type='virtio' /></interface>

5. Save the changes and exit the text editor

6. Restart the guest operating system.

Creating new guests using other network driversAlternatively, new virtualized guests can be created with a different network driver. This may berequired if you are having difficulty installing guests over a network connection. This method requiresyou to have at least one virtualized guest already created (possibly installed from CD or DVD) to useas a template.

1. Create an XML template from an existing virtualized guest (in this example, named Guest1):

# virsh dumpxml Guest1 > /tmp/guest-template.xml

2. Copy and edit the XML file and update the unique fields: virtual machine name, UUID, disk image,MAC address, and any other unique parameters. Note that you can delete the UUID and MACaddress lines and virsh will generate a UUID and MAC address.

# cp /tmp/guest-template.xml /tmp/new-guest.xml# vi /tmp/new-guest.xml

Add the model line in the network interface section:

<interface type='network'> [output truncated] <model type='virtio' /></interface>

3. Create the new virtual machine:

# virsh define /tmp/new-guest.xml# virsh start new-guest

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Appendix A. Additional resourcesTo learn more about virtualization and Red Hat Enterprise Linux, refer to the following resources.

A.1. Online resources• http://www.libvirt.org/ is the official website for the libvirt virtualization API.

• http://virt-manager.et.redhat.com/ is the project website for the Virtual Machine Manager (virt-manager), the graphical application for managing virtual machines.

• Open Virtualization Center

http://www.openvirtualization.com1

• Red Hat Documentation

http://www.redhat.com/docs/

• Virtualization technologies overview

http://virt.kernelnewbies.org2

• Red Hat Emerging Technologies group

http://et.redhat.com3

A.2. Installed documentation• man virsh and /usr/share/doc/libvirt-<version-number> — Contains sub commands

and options for the virsh virtual machine management utility as well as comprehensive informationabout the libvirt virtualization library API.

• /usr/share/doc/gnome-applet-vm-<version-number> — Documentation for the GNOMEgraphical panel applet that monitors and manages locally-running virtual machines.

• /usr/share/doc/libvirt-python-<version-number> — Provides details on the Pythonbindings for the libvirt library. The libvirt-python package allows python developers tocreate programs that interface with the libvirt virtualization management library.

• /usr/share/doc/python-virtinst-<version-number> — Provides documentation onthe virt-install command that helps in starting installations of Fedora and Red Hat EnterpriseLinux related distributions inside of virtual machines.

• /usr/share/doc/virt-manager-<version-number> — Provides documentation on theVirtual Machine Manager, which provides a graphical tool for administering virtual machines.

http://www.libvirt.org/

http://virt-manager.et.redhat.com/

http://www.openvirtualization.com/

http://www.redhat.com/docs/

http://virt.kernelnewbies.org/

http://et.redhat.com/

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GlossaryThis glossary is intended to define the terms used in this Installation Guide.

Bare-metal The term bare-metal refers to the underlying physical architecture of acomputer. Running an operating system on bare-metal is another wayof referring to running an unmodified version of the operating systemon the physical hardware. An example of operating system running onbare metal is a normally installed operating system.

Full virtualization KVM uses full, hardware-assisted virtualization. Full virtualizationuses hardware features of the processor to provide total abstractionof the underlying physical system (Bare-metal) and creates a newvirtual machine in which the guest operating systems can run. Nomodifications are needed in the guest operating system. The guestoperating system and any applications on the guest are not awareof the virtualized environment and run normally. Para-virtualizationrequires a modified version of the Linux operating system.

Fully virtualized See Full virtualization.

Guest system Also known as guests, virtual machines, virtual servers or domains.

Hardware Virtual Machine See Full virtualization

Host The host operating system runs virtualized guests.

Hypervisor The hypervisor is the software layer that abstracts the hardware fromthe operating system permitting multiple operating systems to run onthe same hardware. The hypervisor runs on a host operating systemallowing other virtualized operating systems to run on the host'shardware.

The Kernel-based Virtual Machine hypervisor is provided with RedHat Enterprise Linux.

I/O Short for input/output (pronounced "eye-oh"). The term I/O describesany program, operation or device that transfers data to or from acomputer and to or from a peripheral device. Every transfer is anoutput from one device and an input into another. Devices such askeyboards and mouses are input-only devices while devices such asprinters are output-only. A writable CD-ROM is both an input and anoutput device.

Kernel SamePage Merging Kernel SamePage Merging (KSM) is used by the KVM hypervisorto allow KVM guests to share identical memory pages. The pagesshared are usually common libraries or other identical, high-use data.KSM allows for greater guest density of identical or similar guestoperating systems by avoiding memory duplication.

For information on using KSM with Red Hat Enterprise Linux refer toChapter 21, KSM.

Kernel-based VirtualMachine

KVM (Kernel-based Virtual Machine) is a Full virtualization solutionfor Linux on AMD64 and Intel 64 hardware. KVM is a Linux kernelmodule built for the standard Red Hat Enterprise Linux kernel. KVM

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can run multiple, unmodified virtualized guest Windows and Linuxoperating systems. The KVM hypervisor in Red Hat EnterpriseLinux is managed with the libvirt API and tools built for libvirt, virt-manager and virsh.

KVM is a set of Linux kernel modules which manage devices,memory and management APIs for the Hypervisor module itself.Virtualized guests are run as Linux processes and threads which arecontrolled by these modules.

Red Hat Enterprise Linux KVM hypervisors can be managed by theRed Hat Enterprise Virtualization Manager as an alternative to libvirt.

LUN A Logical Unit Number (LUN) is a number assigned to a logical unit (aSCSI protocol entity).

MAC Addresses The Media Access Control Address is the hardware address for aNetwork Interface Controller. In the context of virtualization MACaddresses must be generated for virtual network interfaces with eachMAC on your local domain being unique.

Migration Migration is the term for the process of moving a virtualized guestfrom one host to another. Migration can be conducted offline (wherethe guest is suspended and then moved) or live (where a guest ismoved without suspending).

Offline migration

An offline migration suspends the guest then moves an image of theguest's memory to the destination host.

Live migration

Live migration is the process of migrating a running guest from onephysical host to another physical host.

Para-virtualization Para-virtualization is only available in Red Hat Enterprise Linux 5.Para-virtualization uses software mechanisms to share devices andsystem resources with specially-designed kernels or newer kernelswith the PV-opts features.

Para-virtualized See Para-virtualization,

Para-virtualized drivers Para-virtualized drivers are device drivers that operate on fullyvirtualized Linux guests. These drivers greatly increase performanceof network and block device I/O for fully virtualized guests.

PCI passthrough The KVM hypervisor supports attaching PCI devices on the hostsystem to virtualized guests. PCI passthrough allows guests tohave exclusive access to PCI devices for a range of tasks. PCIpassthrough allows PCI devices to appear and behave as if they werephysically attached to the guest operating system.

Physical Functions Physical Functions (PFs) are full PCIe devices that include the SR-IOV capabilities. Physical Functions are discovered, managed, andconfigured as normal PCI devices. Physical Functions configure andmanage the SR-IOV functionality by assigning Virtual Functions.

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Security Enhanced Linux Short for Security Enhanced Linux, SELinux uses Linux SecurityModules (LSM) in the Linux kernel to provide a range of minimumprivilege required security policies.

Single Root I/OVirtualization

SR-IOV is a standard for a type of PCI passthrough which nativelyshares a single device to multiple guests.

SR-IOV enables a Single Root Function (for example, a singleEthernet port), to appear as multiple, separate, physical devices. Aphysical device with SR-IOV capabilities can be configured to appearin the PCI configuration space as multiple functions, each device hasits own configuration space complete with Base Address Registers(BARs).


• Physical Functions

• Virtual Functions

Universally Unique Identifier A Universally Unique Identifier (UUID) is a standardized numberingmethod for devices, systems and certain software objects indistributed computing environments. Types of UUIDs in virtualizationinclude: ext2 and ext3 file system identifiers, RAID deviceidentifiers, iSCSI and LUN device identifiers, MAC addresses andvirtual machine identifiers.

Virtual Functions Virtual Functions (VFs) are simple PCIe functions that only processI/O. Each Virtual Function is derived from a Physical Function. Thenumber of Virtual Functions a device may have is limited by thedevice hardware. A single Ethernet port, the Physical Device, maymap to many Virtual Functions that can be shared to virtualizedguests.

Virtual machines A virtual machine is a software implementation of a physicalmachine or programming language (for example the Java RuntimeEnvironment or LISP). Virtual machines in the context of virtualizationare operating systems running on virtualized hardware.

Virtualization Virtualization is a broad computing term for running software, usuallyoperating systems, concurrently and isolated from other programson one system. Most existing implementations of virtualization usea hypervisor, a software layer that controls hardware and providesguest operating systems with access to underlying hardware. Thehypervisor allows multiple operating systems to run on the samephysical system by giving the guest operating system virtualizedhardware. There are various methods for virtualizing operatingsystems:

• Hardware-assisted virtualization is the technique used for fullvirtualization with KVM (definition: Full virtualization)

• Para-virtualization is a technique used by Xen to run Linux guests(definition: Para-virtualization)

• Software virtualization or emulation. Software virtualization usesbinary translation and other emulation techniques to run unmodified

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operating systems. Software virtualization is significantly slowerthan hardware-assisted virtualization or para-virtualization.Software virtualization, in the form of QEMU or BORCH, works inRed Hat Enterprise Linux, it's just slow.

Red Hat Enterprise Linux supports hardware-assisted, fullvirtualization with the KVM hypervisor.

Virtualized CPU A system has a number of virtual CPUs (VCPUs) relative to thenumber of physical processor cores. The number of virtual CPUs isfinite and represents the total number of virtual CPUs that can beassigned to guest virtual machines.

Xen Xen is not available as a hypervisor type for Red Hat Enterprise Linux6 and newer. Xen is only supported for Red Hat Enterprise Linux 5and newer.

Red Hat Enterprise Linux 5 supports the Xen hypervisor and the KVMhypervisor (refer to Kernel-based Virtual Machine). Both hypervisorshave different architectures and development approaches. The Xenhypervisor runs underneath a Red Hat Enterprise Linux operatingsystem which acts as a host managing system resources andvirtualization APIs.

Red Hat Enterprise Linux 6 is supported as a para-virtualized andfully-virtualized guest of Red Hat Enterprise Linux 5.4 (and newer)running the Xen hypervisor. Red Hat Enterprise Linux 6 is alsosupported as a guest of the Red Hat Enterprise Linux 5.4 (and newer)running the KVM hypervisor.

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Appendix B. Revision HistoryRevision6.0-35

Mon Oct 04 2010 Scott Radvan [email protected]

Review for 6.0 release.

Revision6.0-25

Thu Sep 09 2010 Christopher Curran [email protected]

Resolves BZ#6217401.

Revision6.0-24

Fri Sep 03 2010 Christopher Curran [email protected]

Updated para-virtualized driver usage procedures. BZ#6217402.

Revision6.0-23

Tue May 25 2010 Christopher Curran [email protected]

New storage content BZ#5368163.

Revision6.0-22

Fri May 14 2010 Christopher Curran [email protected]

Fixes BZ#5879114, which expands supported storage devices.Updated Introduction chapterUpdated Troubleshooting chapterUpdated KSM chapterUpdated overcommitting guidance.

Revision6.0-11

Tue Apr 20 2010 Christopher Curran [email protected]

Beta version update. Various fixes included.

Revision6.0-10

Thu Apr 15 2010 Christopher Curran [email protected]

Forward-ported the following fixes from the Red Hat Enterprise Linux 5.5 release:Fixes BZ#5735585, and expands SR-IOV content.Fixes BZ#5590526, expands the KVM para-virtualized drivers chapter.Fixes BZ#5783427.Fixes BZ#5735538.Fixes BZ#5735569.Fixes BZ#57354910.Fixes BZ#53402011.Fixes BZ#57355512.

Revision 6.0-5 Mon Mar 01 2010 Christopher Curran [email protected]

mailto:[email protected]




















Appendix B. Revision History

318

Beta version released.

319

Appendix C. ColophonThis manual was written in the DocBook XML v4.3 format.

This book is based on the original work of Jan Mark Holzer, Justin Clift and Chris Curran.

This book is edited and maintained by Scott Radvan.

Other writing credits go to:

• Daniel Berrange contributed various sections on libvirt.

• Don Dutile contributed technical editing for the para-virtualized drivers section.

• Barry Donahue contributed technical editing for the para-virtualized drivers section.

• Rick Ring contributed technical editing for the Virtual Machine Manager Section.

• Michael Kearey contributed technical editing for the sections on using XML configuration files withvirsh and virtualized floppy drives.

• Marco Grigull contributed technical editing for the software compatibility and performance section.

• Eugene Teo contributed technical editing for the Managing Guests with virsh section.

Publican, the publishing tool which produced this book, was written by Jeffrey Fearn.

TranslatorsDue to technical limitations, the translators credited in this section are those who worked on previousversions of the Red Hat Enterprise Linux Virtualization Guide and the Fedora Virtualization Guide.

To find out who translated the current version of the guide, visit https://fedoraproject.org/wiki/Fedora_13_Documentation_Translations_-_Contributors. These translators will receive credit insubsequent versions of this guide.

• Simplified Chinese

• Leah Wei Liu

• Traditional Chinese

• Chester Cheng

• Terry Chuang

• Japanese

• Kiyoto Hashida

• Korean

• Eun-ju Kim

• Dutch

• Geert Warrink

• French

https://fedoraproject.org/wiki/Fedora_13_Documentation_Translations_-_Contributors

https://fedoraproject.org/wiki/Fedora_13_Documentation_Translations_-_Contributors

Appendix C. Colophon

320

• Sam Friedmann

• German

• Hedda Peters

• Greek

• Nikos Charonitakis

• Italian

• Silvio Pierro

• Francesco Valente

• Brazilian Portuguese

• Glaucia de Freitas

• Leticia de Lima

• Spanish

• Domingo Becker

• Héctor Daniel Cabrera

• Angela Garcia

• Gladys Guerrero

• Russian

• Yuliya Poyarkova

Documents

Virtualization Guide - Guide to Virtualization on Red Hat ...fcs/Doc/RedHat/Red_Hat_Enterprise_Linux-6... · Red Hat Enterprise Linux 6 Virtualization Guide Guide to Virtualization